[Feat] Add repository search to environment setup

[roomote-community]

​Opened on behalf of @tomny-dev. View the task or mention @roomote for follow-up asks.

What changed

• added case-insensitive repository search to the shared environment repository selector
• preserved selected repositories while filters hide them and restored their checked state when search is cleared
• kept repository creation available during no-match searches and added a clear empty-result state
• kept onboarding on its existing thresholded repository filter instead of rendering a second search field
• added client coverage for filtering, selection persistence, no-match behavior, empty repository lists, and caller-owned filters

Why this change was made

Environment setup currently renders every connected repository in one scrollable list. Searching by owner or repository name makes the intended repository practical to find when an account has many connected repositories.

Impact

Users can now filter repositories while creating or editing an environment without additional network requests or changes to the selected repository set. Onboarding continues to show only its existing filter. The 43 focused tests, full web client suite with 1,809 tests, web type checking, web lint, and repository pre-push checks pass. Browser screenshots could not be captured because mandatory inference setup prevented reaching repository selection on the local product surface.

[roomote-community]

No code issues found. See task

• EnvironmentRepositorySelector.tsx:57: Avoid rendering a second repository filter in onboarding.

_{Reviewed d00f7a5}

[roomote-community]

Fixed the duplicate onboarding repository filter and the failing Test check in 8f7cfa2. Onboarding now suppresses the shared selector search and retains only its existing thresholded filter; the missing test mock is also covered. The 43 focused tests, full 1,809-test web client suite, type checking, lint, and pre-push checks pass. Visual proof remains blocked by mandatory inference setup before repository selection. See task.