docs: ADR-0005 install seam + Origin model (spec 003 groundwork); gitignore specs/

[aroff]

Summary

Design groundwork for browser skill management (spec 003), settled via a grilling session. This PR is docs + repo-hygiene only — no code changes (the implementation follows in later phases on this branch).

It also flips how design specs are stored: specs/ becomes a local working artifact rather than shipped in the repo.

What's here

• docs/adr/0005-install-seam-and-origin-model.md — the architectural spine:
  • Install/update/reindex logic moves into fastskill-core; the CLI (execute_add/execute_update/execute_reindex) becomes a thin caller over the same core methods — one path, no drift. The embedding provider is injected at serve startup; the HTTP path returns structured results (no shell-out, no 501). UpdateService is narrowed to the read-only "what's newer?" query.
  • One canonical Origin enum (git | local | zip-url | repository) replaces SkillSource (two colliding types), SourceType, and the nine flat SkillDefinition.source_* fields. Origin::repository is a reference into a configured Repository, not the Repository itself. Greenfield break, no back-compat shim.
  • Records the rejected alternatives (trait-injection; keep shelling out; leave the CLI on a separate path).
• CONTEXT.md — new Origin glossary term + the Origin::repository ≠ Repository distinction.
• .gitignore — specs/ are local design artifacts; untrack the existing specs (they remain on disk + in history).

Key resolved decisions (from the grill)

Branch	Decision
Seam	Move logic to core; inject the embedding provider; migrate the CLI onto the shared method
Origin	One canonical enum; full reconciliation; greenfield break, no shim
Install≡Update	One install(origin, mode: Fresh|Update); per-variant re-resolve; immutable/editable = honest no-ops
Identity	Derived id; install is fetch-then-409-on-existing-id (even for a different Origin)
Reindex	Auto iff provider else skip-silently; standalone /reindex → 200 skipped (not 501) with no provider
Capabilities	GET /status gains writable + embedding_provider; 403 stays as backstop
Phasing	0 Origin model → 1 core seams + CLI migration → 2 endpoints → 3 UI → v2 (version picker, sanitized MD preview)

Note

The rewritten specs/003-browser-skill-management.md now lives on disk only (gitignored), so it is intentionally not in this diff. The ADR + glossary are the committed design record; the implementation phases land on this branch next.

Pre-commit checks pass (fmt / clippy -D warnings / 658 tests — code unchanged from main).

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