chore: docs + a11y housekeeping wave (closes #910, #925, #949, #950, #951)

[Salem874]

Summary

Tight follow-up wave to PR #947 — closes 5 issues (3 newly identified during the audit-discovery workflow wv461v32a, 2 from the existing backlog whose trigger conditions are met) plus drops 3 more (#936 / #885 / #886) via batched issue close. Mostly docs + a11y polish; zero behaviour change.

What's included

#949 — Milestone numbering fix (6 files)

The authoritative milestone table at Project_Plan.md:358-362 was renumbered at some point (BBC iPlayer bumped to M8, Spotify to M9, YouTube to M10) but six other files plus Project_Plan.md's own per-milestone section headers + prose bullets still carried the legacy numbering (Spotify=M8, YouTube=M9, BBC iPlayer=M10).

Bug surfaces in user-facing Help — clicking the in-app Help > Supported Services or reading help/supported-services.md showed the wrong service mapped to v2.0.0 / v2.1.0 / v2.2.0.

13 single-line edits across:

• `src-tauri/src/services/engine_runner.rs` — 3 stub builder error messages + 3 doc-comment lines
• `src-tauri/src/models/settings.rs` — 2 doc-comment lines
• `src/types/index.ts` — 2 comment annotations
• `src/components/help/HelpViewer.tsx` — 3 user-visible heading lines
• `help/supported-services.md` — 3 section heading lines
• `Project_Plan.md` — 3 section headers + 2 prose bullets

#925 + #910 — GAMDL audit docs backfill

CLAUDE.md carried full per-commit admission paragraphs for v3.7.2, v3.7.3, and v3.7.4, but the corresponding standalone audit docs under `.github/audits/` were never written. This PR lifts the existing prose into the established audit-doc format used by gamdl-v3.5.2-audit.md:

• `.github/audits/gamdl-v3.7.2-v3.7.3-audit.md` — pair of bug-fix releases shipped same-day (2026-05-28); documents the uncensored MV title/album switch + defensive `.get('playParams')` access + the one MeedyaDL code change required (`is_media_not_streamable_error` classifier).
• `.github/audits/gamdl-v3.7.4-audit.md` — 4-functional-commit reliability patch (2026-06-12); HLS variant rewrite + AMP token regex + cover-fetch HTTP hardening + API exception content typing. Zero-code-change admission.

Closes #910 (whose body declared its own close-trigger as "when upstream tags 3.7.4 and MeedyaDL ships the admission PR" — condition met by PR #947's version bump + this doc backfill).

#951 — console.log → console.debug

src/App.tsx:950 deep-link handler logged via `console.log`. The prevailing convention elsewhere is `console.debug` (`src/hooks/useTheme.ts:188-196`, `src/main.tsx:90`) so dev-only diagnostics are suppressed at the browser's default log level. Line above already shows a user-facing toast, so the console line is purely dev-diagnostic.

#950 — Cancel/Retry tooltip a11y

Sibling to #945. The Cancel + Retry buttons in QueueItem had `title="Cancel"` / `title="Retry"` but `aria-label="Cancel download" / "Retry download"` — sighted-hover tooltip didn't match screen-reader announcement. Updated `title` to the longer form so both match.

Sibling issue triage (parallel close, not in this PR)

These were closed via `gh issue close` during the housekeeping wave:

• fix(lyrics): syllable-lyrics fetch silently degrades to line-level — missing extend=ttmlLocalizations + Origin header + ttmlLocalizations fallback (PR-2) #936 — closed as duplicate of feat(lyrics): word/syllable-level TTML granularity classifier + per-track Step 1b decision matrix (PR-3) #935 (the HTTP-layer syllable-lyrics fix shipped in fix: bundled audit hardening + #935 syllable lyrics + #937 release pipeline + repo hygiene (closes #935, #937, #938-#946) #947's bundle; fix(lyrics): syllable-lyrics fetch silently degrades to line-level — missing extend=ttmlLocalizations + Origin header + ttmlLocalizations fallback (PR-2) #936 was a sibling issue split during scope-planning).
• Audit + maybe-cherry-pick commands/download.rs from prep/expanded-services-groundwork #885 — closed (not planned) per the issue body's own "Defer until M8 starts" recommendation. Re-evaluate when Support for BBC iPlayer #102 work begins.
• Audit + maybe-cherry-pick models/download_options.rs from prep/expanded-services-groundwork #886 — closed (not planned) for the same reason as Audit + maybe-cherry-pick commands/download.rs from prep/expanded-services-groundwork #885.

Verification

• ✅ `cargo check` clean (engine_runner.rs + settings.rs string changes only)
• ✅ `npm run type-check` clean (types/index.ts + App.tsx + QueueItem.tsx are doc-comment + tooltip + console-method edits)
• ✅ `rg M8.*BBC|M9.*Spotify|M10.*YouTube help/supported-services.md Project_Plan.md src/components/help/HelpViewer.tsx` confirms the new mapping; inverse grep returns empty
• ✅ Project_Plan.md table at L358-362 unchanged (was already correct)
• ✅ `.github/audits/` ls shows v3.5.2, v3.5.1, v3.4-v3.5, v3.2, and now v3.7.2-v3.7.3 + v3.7.4 — cumulative coverage complete for the support window

Test plan

• fix(docs): M8/M9/M10 milestone numbering scrambled across 6 files — visible in in-app Help #949 Open in-app Help > Supported Services — verify the visible roadmap reads "Spotify v2.1.0", "YouTube v2.2.0", "BBC iPlayer v2.0.0".
• fix(docs): M8/M9/M10 milestone numbering scrambled across 6 files — visible in in-app Help #949 Paste a Spotify URL with no M9 build — engine_runner error toast should say "planned for v2.1.0" (was v2.0.0).
• audit: admit GAMDL v3.7.4 (zero-code-change, reliability patch) #925 Check both new audit docs render correctly on GitHub.
• chore(frontend): console.log → console.debug in App.tsx deep-link handler #951 With browser devtools log level set to default (info), paste a `meedyadl://` deep link — "Deep link received: …" line should NOT appear in console. Switch log level to verbose → it appears.
• a11y(QueueItem): align Cancel/Retry button tooltips with aria-label (sibling to #945) #950 Hover Cancel/Retry on a queue item — tooltip says "Cancel download" / "Retry download" (was "Cancel" / "Retry"). VoiceOver still announces the long form (was already correct via aria-label).

🤖 Generated with Claude Code

[github-actions]

PR Security Checks

⚠️ 1 category(ies) of findings — these are heuristics, please review each:

Hardcoded absolute filesystem paths (derive from app_data_dir / std::env, not literals)

src/components/download/QueueItem.tsx:332:         * Example: '/Users/me/Music/Artist/Album/01 Track.m4a'
src/components/download/QueueItem.tsx:333:         *       -> '/Users/me/Music/Artist/Album'

_{Generated by .github/workflows/pr-security.yml. Non-blocking — the merge gate is ci.yml. Cross-source checks live in tools/audit-checks/ and run locally. False positives are expected.}

[Salem874]

Superseded by PR #954 (combined alpha-targeting housekeeping).

After auditing this PR's 4 commits against the actual alpha codebase:

• 21c226fe milestone numbering — alpha already has M9-1..M9-6 correctly applied (set during M9 Spotify integration work). The bug only ever existed on main and will resolve naturally when alpha→main flow happens.
• 99b5d0fc GAMDL v3.7.2-v3.7.3 + v3.7.4 audit docs — already exist on alpha (came in via PR feat(brand): brand refresh + logotype→wordtype rename + GAMDL v3.7.4 admission + dep bumps (supersedes #929, #931, closes #925) #928 brand refresh + GAMDL admission).
• 205f1526 console.debug — landed in PR chore(alpha): combined housekeeping — console.debug + tooltip a11y + ffprobe noise filter (closes #847, #950, #951; supersedes #952 #953) #954.
• ea9b133f Cancel/Retry tooltip a11y — landed in PR chore(alpha): combined housekeeping — console.debug + tooltip a11y + ffprobe noise filter (closes #847, #950, #951; supersedes #952 #953) #954.

Closing per user instruction to consolidate housekeeping into a single alpha-targeting merge.