Add run treemap visualization

[dutifulbob]

Summary

• add duration-aware run treemap contracts, data model fields, and API endpoint
• render a treemap on run detail pages with step, file, and process drill-down
• cover the treemap endpoint in integration tests and verify the UI drill-down flow

Testing

• pnpm format:check
• pnpm lint
• pnpm docs:validate
• pnpm typecheck
• pnpm test
• pnpm build
• DATABASE_URL=postgresql://verge:verge@127.0.0.1:54329/verge VERGE_INTEGRATION_DATABASE_URL=postgresql://verge:verge@127.0.0.1:54329/verge GITHUB_WEBHOOK_SECRET=integration-secret pnpm test:integration
• DATABASE_URL=postgresql://verge:verge@127.0.0.1:54329/verge GITHUB_WEBHOOK_SECRET=integration-secret pnpm test:smoke

[dutifulbob]

Implemented the run treemap end to end.

What changed:

• added run treemap contracts and API support
• added stored duration_ms on runs, step runs, and process runs
• added a dedicated /runs/:id/treemap read model that builds run -> step -> file -> process
• added the treemap UI on the run page with step/process drill-through
• fixed duration handling so active items still show live elapsed time when stored duration is absent
• handled treemap fetch failures without breaking the rest of the run page
• added process-row highlighting when navigating from the treemap into a step detail view

Validation run on the current head:

• pnpm format:check -> passed
• pnpm lint -> passed
• pnpm docs:validate -> passed
• pnpm typecheck -> passed
• pnpm test -> passed
• pnpm build -> passed
• DATABASE_URL=postgresql://verge:verge@127.0.0.1:54329/verge VERGE_INTEGRATION_DATABASE_URL=postgresql://verge:verge@127.0.0.1:54329/verge GITHUB_WEBHOOK_SECRET=integration-secret pnpm test:integration -> passed
• DATABASE_URL=postgresql://verge:verge@127.0.0.1:54329/verge GITHUB_WEBHOOK_SECRET=integration-secret pnpm test:smoke -> passed

Browser verification:

• verified the treemap on a branch-local instance with an isolated database
• verified step-node navigation from the treemap into step detail
• verified process-node navigation into a highlighted process row on the step page
• verified there were no page errors during the checked flows

Review:

• pushed the latest head before review
• ran codex review --base main
• fixed the issues it surfaced around duration fallback and treemap error handling
• reran review on the updated head; no additional P0/P1 findings surfaced in the emitted review trace after the fixes

What was not fully verified locally:

• staging or production deployment behavior
• cross-browser verification beyond the local browser automation run