perf: add first-turn timing diagnostics for new-tab sessions

[luoxuanzao]

Summary

• Adds [qoderian perf] timing logs across the new-tab → first-session chain so slow first replies can be attributed to a concrete stage instead of guesswork.
• Instrumented stages: tab.create / tab.restore / tab.switchTo, turn.buildSubmission / turn.titleGeneration / turn.serviceInit / turn.prepareTurn, runtime.spawnPersistentQuery, runtime.cliFirstMessage (CLI cold-start), runtime.applyDynamicUpdates, turn.enqueueToFirstChunk, plus end-to-end turn.firstChunk / turn.total and the background title.coldStartQuery.
• Pure instrumentation — no behavior changes. Labels are fixed stage names without user data, so logs are safe to paste into bug reports.

Verification

• npm run typecheck
• npm run lint
• npm run test (3481 tests)
• npm run build
• npm run release:check
• npm run audit:prod (0 vulnerabilities)
• Tested affected qodercli behavior against a real CLI when applicable (n/a — instrumentation only; SDK mock covers the message flow)

Safety

• No credentials, private vault content, internal URLs, or personal paths are included
• User-visible changes are documented in CHANGELOG.md