Add: high-level design doc with Mermaid diagrams

[0xLeif]

Summary

• Add docs/HLD.md, a high-level design of fledge written from the code: command dispatch (including how unknown verbs become plugin commands), fledge.toml, task and lane execution, the plugin system (install, manifest, registry, fledge-v1 protocol, WASM sandbox), work, release and the GitHub plugin, hooks, data and file locations, deployment, the trust model, failure modes and limits, and the decisions in specs/*/context.md. Every section links to the source files it describes.
• 14 Mermaid diagrams: context, module map, dispatch, sequence diagrams for fledge run, fledge lanes run, plugin install, plugin invocation, work plus the GitHub plugin, and release, plus hooks, the fledge.toml ER diagram, the plugin manifest and registry class diagram, the release pipeline and trust-tier classification.
• README: a short Architecture section with one overview diagram and a link to the HLD. Nothing else in the README changed.
• Pages is unchanged on purpose. The Astro site built by pages.yml is now redirect-only (every route goes to the CorvidLabs hub), so there is no docs page to add Mermaid to. The HLD is read on GitHub, which renders Mermaid natively.
• hi/ and INTENT.md already exist and are untouched. hi check passes.

Things the HLD records as observed behavior, which may be worth a look separately (no code changed here):

• A Swift repo with no fledge.toml is detected as swift, but auto_detect_tasks has no Swift entry, so fledge run lists no tasks.
• If a post_remove hook fails, plugins remove has already deleted the command links but leaves the plugin dir and registry entry.
• install.sh does not check the release .sha256 sidecar (the GitHub Action does).

Test Plan

• All 14 HLD diagrams and the README diagram render with mmdc (mermaid-cli 12.0.0)
• All 72 relative file links in docs/HLD.md resolve
• hi check passes (197 criteria, 10 families)
• fledge lanes run verify passes (fmt, lint, test, build, spec-check, validate-templates)
• fledge trust verify --range origin/main..HEAD passes (verify-native lane, contract, risk proceed at 28, provenance soft)
• specsync change check --strict --require-coverage 100 passes
• CI green on this PR

🤖 Generated with Claude Code

https://claude.ai/code/session_01V3ZZAEiUP7xRJPozhZb6rL

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[github-actions]

✅ Corvin says...

      _
    <(^\  .oO(Caw! ^v^)
     |/(\
      \(\\
      " "\\

"Caw! Found a shiny new spec!"

CI Summary

Check	Status
Dependency Audit	✅ Passed
Integration (3 OS)	✅ Passed
Lint (fmt + clippy)	✅ Passed
Spec Validation	✅ Passed
Tests (3 OS)	✅ Passed

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