[REQ-135][CODE] Refresh desktop catalog snapshot after community Excel retirement #1027

Covers

Parent alpha-work#65 AC1 and AC2 (desktop snapshot homology half).

alpha-web#155 / PR #156 already removed mcp:excel from the signed catalog (2026-08-17.3). Desktop still ships alpha-catalog.json 2026-08-06.1, which contains mcp:excel; Hub filters it (alpha-catalog.test.ts currently asserts the stale bytes on purpose). Offline/fallback therefore still carries the retired card until the snapshot is refreshed.

Boundary

• packages/ui-mac/scripts/sync-catalog-snapshot.mjs (prefer --from-file against local alpha-web public/catalog/v1/catalog.json + .sig if alphacodeone.com times out)
• packages/ui-mac/src/renderer/extensions/alpha-catalog.json
• packages/ui-mac/src/renderer/extensions/alpha-catalog.snapshot.json
• packages/ui-mac/src/renderer/extensions/alpha-catalog.test.ts (flip the “still contains community Excel” test to absence + installable-view still denies)

Do not hand-edit catalog bytes. Do not reopen #1012.

Out of scope

Catalog authoring, Hub UI copy, new Excel connectors, bumping a signed desktop release.

Exit condition

Merged PR + local bin/check green. alpha-catalog.test.ts asserts the snapshot has no mcp:excel / excel-mcp-server, bundle:office members match the signed catalog, and sha256 matches snapshot meta.

Parent

Refs jinjunnn/alpha-work#65 (native sub-issue; never a closing keyword against the parent)