fix(docs): M8/M9/M10 milestone numbering scrambled across 6 files — visible in in-app Help

[Salem874]

Problem

The authoritative milestone table in Project_Plan.md:358-362 says:

Milestone	Version	Service	Engine
M8	v2.0.0	BBC iPlayer	get_iplayer / yt-dlp
M9	v2.1.0	Spotify	votify
M10	v2.2.0	YouTube	yt-dlp

But six other files (and Project_Plan.md's own per-milestone sections + prose bullets) still carry the LEGACY numbering pattern (Spotify=M8, YouTube=M9, BBC iPlayer=M10) from before BBC iPlayer was bumped to M8. The mismatch is visible to users in the in-app Help viewer.

Affected files

• src-tauri/src/services/engine_runner.rs — 3 stub builder error messages + 3 doc-comment lines (Votify says M8/v2.0.0 → should be M9/v2.1.0; yt-dlp says M9/M10 + v2.1.0 → should be M8/M10 + v2.0.0/v2.2.0; get_iplayer says M10/v2.2.0 → should be M8/v2.0.0)
• src-tauri/src/models/settings.rs:519-530 — Votify says M8/v2.0.0; yt-dlp says M9/v2.1.0
• src/types/index.ts:861-866 — "(stub for M8)" on Spotify; "(stub for M9)" on YouTube
• src/components/help/HelpViewer.tsx:982-1019 — USER-FACING in the Help page; Spotify v2.0.0 / YouTube v2.1.0 / BBC iPlayer v2.2.0
• help/supported-services.md:40-69 — USER-FACING help markdown; Spotify M8/v2.0.0 / YouTube M9/v2.1.0 / BBC iPlayer M10/v2.2.0
• Project_Plan.md:375-471 — Section headers + line 529 + line 570 (prose bullets) use the legacy numbering even though the table at 358-362 is correct

Severity

Bug. The user-facing Help viewer + supported-services help doc display incorrect roadmap information. Users planning around the milestone schedule (or just curious which service ships next) see the wrong service mapped to v2.0.0 / v2.1.0 / v2.2.0.

Fix

Single PR with 13 line edits applying the new mapping consistently:

M8 = v2.0.0 = BBC iPlayer = get_iplayer / yt-dlp
M9 = v2.1.0 = Spotify     = votify
M10 = v2.2.0 = YouTube     = yt-dlp

No code-behaviour change — purely string/doc consistency.

Verification

• rg -n "M8|M9|M10|v2\\.[012]\\.0" <files> returns the new mapping in every hit.
• Project_Plan.md table at 358-362 unchanged (it was already correct).
• Build clean.