Add: docs/HLD.md, the high-level design, with its diagrams on Pages

[0xLeif]

Summary

• Adds docs/HLD.md, a high-level design written from the code: purpose, context, components, key flows, data, runtime and deployment, trust boundaries, failure modes, decisions and a glossary. It links DECISIONS.md and HI-1.md rather than restating them, and marks what this repository cannot answer as Unknown: (the Homebrew tap and the corvidlabs.xyz docs site both live elsewhere).
• 12 Mermaid diagrams: context, modules, argv routing, sequence diagrams for capture, retire, export and the fledge plugin and its hooks, the INTENT.md feature-list rewrite, how parse_body classifies a line, a state diagram of an id's standing (not a lifecycle, per DECISIONS §5), the in-memory model, and build, release and Pages.
• Pages: pages.yml now also renders the HLD to /architecture/. It converts the markdown with a pinned marked and splices it into docs/site/architecture.html, which draws the diagrams with Mermaid from jsdelivr, fixes relative links to point at GitHub, and gives headings GitHub-style ids. It is a separate page on purpose: the hi view intent page fetches nothing (VIEW-2), so Mermaid does not belong in hi's renderer, and index.html, intent.html and intent.json are unchanged. The path filter adds docs/HLD.md and docs/site/**.
• README: a short Architecture section with one overview diagram and links to the HLD and the live page. Nothing else in the README changed.
• No source, test, spec or hi/ changes. hi/ already existed, so only hi check was run.

Test Plan

• fledge lanes run verify passes (fmt, clippy, 229 tests, view-behaves 14 checks, intent, index, specsync 10/10, nudge-behaves, plugin validate)
• hi check: 168 criteria, 10 families, 7 files, 2 retired, no problems, no notes
• Every diagram in docs/HLD.md (12) and README.md (1) renders with mmdc, with no syntax-error output
• The Pages render step, run locally (the awk splice also under Ubuntu's mawk in Docker, byte-identical): 12 SVGs drawn in headless Chrome, no horizontal overflow at 375px or 1280px, and zero axe violations (WCAG 2.1 A/AA and best practice) in light and dark
• actionlint passes on pages.yml
• After merge: the Pages run succeeds and https://corvidlabs.github.io/hi/architecture/ shows the diagrams

🤖 Generated with Claude Code

https://claude.ai/code/session_01V3ZZAEiUP7xRJPozhZb6rL