Add trace analysis suggestions panel

[liurenfeng94-ops]

Fixes #42

• scan processed trace trees for common performance patterns
• surface suggestions for depth-limit events, expensive type relation checks, hot locations, and dense file checks
• show suggestions in the webview with a jump-to-source action when location data is available
• add focused tests for the suggestion heuristics

Validation:

• pnpm vitest run test/trace-suggestions.test.ts
• pnpm typecheck
• pnpm exec eslint .
• pnpm build