refactor(reconcile): consume @intentius/chant/reconcile primitive (#20)

[lex00]

Closes #20. The cross-repo other half of the in-repo extraction (#38).

Now that chant ships the provider-agnostic reconcile primitive (chant#502, released as @intentius/chant@0.9.0), warden consumes it instead of vendoring its own copy.

Changes

• Bump @intentius/chant and @intentius/chant-lexicon-github to ^0.9.0.
• src/reconcile/core.ts is now a thin re-export of @intentius/chant/reconcile (export * from …). The in-repo import surface is unchanged — diff.ts, guardrails.ts, and index.ts still import from ./core.js, so the 13 cycles and the guardrail layer are untouched.
• The shared primitive's public API is identical to the extracted core, so no call sites changed.

Why this closes #20

The reconcile core (change-set model, diffCollection, guardrail framework) now lives in one place — chant — and every git-host warden (github, and future gitlab/forgejo) consumes @intentius/chant/reconcile rather than vendoring. The deferral condition ("a second git-host warden exists") is moot now that the seam is shared.

Verification

• npx tsc --noEmit clean
• npm test green (468 tests; core.test.ts retained as an integration check that the consumed primitive behaves as expected)
• Action bundle rebuilt — the chant primitive is inlined by esbuild (8 references to diffCollection/runGuardrailChecks in the bundle)
• @intentius/chant@0.9.0 + @intentius/chant-lexicon-github@0.9.0 confirmed live on npm

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