feat(web): harden responsive workspace layout

[redxzeta]

Summary

• add a shared 36rem conversation / 26rem dock workspace layout contract
• temporarily suppress (without overwriting) the preferred left sidebar when all desktop surfaces cannot fit, then restore it automatically
• clamp and restore dock widths from live shell measurements across viewport and container resizing
• keep the Environment panel above the measured composer footprint
• add focused contract coverage and a 1440x900 / 1024x768 full-app browser geometry regression, including Fork Tools disclosure behavior from Group Fork Tools and Fork Lore in Environment with progressive disclosure #136

Closes #126

Verification

• npx --yes bun@1.3.12 run --cwd apps/web test -- workspaceLayout.test.ts — 5 tests passed
• targeted Bun syntax bundle of every changed TypeScript/TSX entry — passed
• git diff --check — passed
• focused browser scenario — Chromium dependencies resolved, then local Vite transform exceeded the container's ~2 GB Node heap before tests ran
• web production build — local Vite transform exceeded the same ~2 GB Node heap

Exact-head GitHub CI is required for format, lint, typecheck, full tests, browser tests, and build before merge.

Review notes

• The responsive contract activates at the supported 1024px desktop floor; narrower/off-canvas behavior is unchanged.
• Sidebar suppression is derived presentation state only. It never writes the user's open/closed preference.
• Dock process/resource lifecycle is unchanged here and remains scoped to Audit and bound retained right-dock surfaces during long coding sessions #130.