fix(github): complete install when app JWT getInstallation 404s

[kilo-code-bot]

Summary

• GitHub App install callbacks reported GET /app/installations/{id} 404s as Sentry errors even after the user-token admin check had already found the installation.
• Install and update flows now persist the installation returned by GET /user/installations, which avoids the app-JWT lookup that can 404 due to GitHub replication lag right after install. Selected repositories are listed with the same user token.
• Remaining app-JWT 404s (non-install setup actions) are logged as warnings instead of exceptions.

Fixes KILOCODE-WEB-27TD

Test plan

• Unit coverage for findAdministeredInstallation returning the matching installation or null
• Callback coverage that install succeeds from the user-token installation even when app-JWT getInstallation would 404
• Callback coverage that a non-install 404 redirects with installation_not_found and does not call captureException

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• apps/web/src/app/api/integrations/github/callback/route.ts
• apps/web/src/app/api/integrations/github/callback/route.test.ts
• apps/web/src/lib/integrations/platforms/github/app-selector.ts
• apps/web/src/lib/integrations/platforms/github/app-selector.test.ts

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_{Reviewed by grok-4.6 · Input: 137K · Output: 12.2K · Cached: 312.6K}

_{Review guidance: REVIEW.md from base branch main}