Daxia [ T3 Code ] Add sidebar resize reset and bounds

[daxia778]

/claim #840

Summary

• Set the thread sidebar default width to 280px with 200px/500px resize bounds.
• Added a double-click reset path on the resize rail while preserving existing drag persistence and collapsed/mobile behavior.
• Added focused SSR and browser tests for the resize affordance, persisted width restore, and reset-to-default behavior.

Demo

https://github.com/daxia778/Bounty-Hunters/releases/download/issue-840-demo-589be91e/t3-sidebar-840-demo-589be91e.mp4

Validation

• npx -y bun@1.3.11 run --cwd apps/web test src/components/ui/sidebar.test.tsx
• npx -y bun@1.3.11 run --cwd apps/web test:browser src/components/ui/sidebar.browser.tsx
• npx -y bun@1.3.11 run --cwd apps/web typecheck
• npx -y bun@1.3.11 run fmt:check apps/web/src/components/AppSidebarLayout.tsx apps/web/src/components/ui/sidebar.tsx apps/web/src/components/ui/sidebar.test.tsx apps/web/src/components/ui/sidebar.browser.tsx apps/web/src/components/.provenance.json
• git diff --check

[github-actions]

Unfortunately the changes in this PR didn't fully resolve the issue. Please rework your solution and submit a new pull request.

Make sure to review the acceptance criteria in the linked issue and verify all conditions are met before resubmitting. See CONTRIBUTING.md for guidelines.