fix(server): await catalog readiness for reads

[harshmathurx]

Issue for this PR

Closes #36117

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Makes the public catalog read handlers wait for the existing plugin readiness barrier before returning successful catalog snapshots:

• /api/model now waits for the same bounded catalog readiness path as /api/model/default.
• /api/provider and /api/provider/{providerID} also wait for plugin readiness before reading provider availability.
• Readiness timeout remains explicit via ServiceUnavailableError instead of returning a successful partial catalog.

This keeps cold-start provider/model reads from treating intermediate plugin/catalog state as authoritative.

@kitlangton tagging you since you authored the issue and the repro. Could you assign #36117 to me if this matches the intended fix direction?

How did you verify your code works?

• Ran git diff --check.
• Attempted the linked focused regression command from packages/server; this branch does not currently include test/catalog-readiness.test.ts, so Bun reported that the filter matched no files.
• Attempted bun run typecheck from packages/server; blocked locally because dependencies/tooling are unavailable (tsgo: command not found) after the repo dependency install is blocked by the private/403 ghostty-web dependency.

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally where possible
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[harshmathurx]

Hi @kitlangton — pinging you on this since it's been a couple of days with no maintainer response. The issue is linked in the PR description and all automated checks are green, but the PR is still waiting on review/merge. Could you take a look when you have a chance? Thanks!