POST /api/updates/apply returns 202 (not 200) on accepted async work

[thinmintdev]

What to build

Routes that accept async work and return a queued-job snapshot use status_code=202 (e.g. /api/models/{id}/pull). /api/updates/apply is the same shape — returns a queued job — but returns 200. Minor inconsistency.

Add status_code=202 to the route decorator.

Acceptance criteria

• POST /api/updates/apply returns 202 on accepted requests
• Failure paths (e.g. invalid input, rate-limit) still return their existing 4xx codes
• No client-facing breakage (clients accepting 2xx)

Blocked by

None - can start immediately

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Sourced from tests/harness/FINDINGS.md §24 (trivial).