Improve launch performance: skip redundant per-launch spawns and writes

[leo-3889]

Summary

Speeds up app launch (especially warm launches) by eliminating redundant per-launch work in the Claude provider:

• Skip unchanged hook-script and settings.json writes on warm launch and profile spawns — the files are only rewritten when their content actually changes, so a warm launch no longer rewrites (and re-watches) them every time.
• Cache the resolved Claude CLI version across launches — the version is resolved once and reused, skipping the per-launch --version spawn.
• Defer PATH resolution / binary-fallback spawn until a fallback binary actually needs to be resolved, instead of doing it up front on every launch.

Testing

• npm run build — all three targets compile.
• npm test — 1868 pass. The one failure is a pre-existing, environment-specific Windows locale issue in big-initial-context.test.ts (expects 50,000, gets 50.000); unrelated to these changes and present on upstream main too.
• New/updated unit tests cover the version cache, binary resolution, and hook-script write-skip logic (claude-version.test.ts, resolve-binary.test.ts, hook-commands.test.ts, claude-cli.test.ts).