Implement Chat MVP session history

[AbigailDeng]

Summary

• Add Chat as the first top-level navigation entry before My Teams and Platform items.
• Wire the Chat MVP to POST /api/chat with local session history stored in the browser.
• Support the Plan -> Confirm -> Create flow, same-session confirmation, direct-create prompts, structured Studio/Team jump targets, and local history restore/rename/delete.
• Add focused coverage for chat API parsing, local history, Chat page state flow, route visibility, and navigation order.

Notes

This implementation branch was created from feat/2026-07-01_chat-page-implementation, so the PR also includes the simplified PRD/prototype commits already on that branch.

Closes #2573

Validation

• corepack pnpm --dir apps/aevatar-console-web tsc
• corepack pnpm --dir apps/aevatar-console-web test:ui
• corepack pnpm --dir apps/aevatar-console-web build

FKST provenance

• Skill: aevatar-frontend-fkst
• Issue: Implement Chat MVP session creation and local history #2573
• Worktree: /Users/xiezixin/Documents/work/aevatar-chat-page
• Branch: feat/2026-07-01_chat-mvp-session-history
• Operator: AbigailDeng
• Freshness: Current user-selected implementation request from 2026-07-01 based on simplified Chat MVP PRD

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.83%. Comparing base (a328d54) to head (a43d4a0).

@@           Coverage Diff           @@
##              dev    #2575   +/-   ##
=======================================
  Coverage   83.82%   83.83%           
=======================================
  Files        1243     1243           
  Lines       95334    95334           
  Branches    12501    12501           
=======================================
+ Hits        79913    79919    +6     
+ Misses       9866     9862    -4     
+ Partials     5555     5553    -2     

Flag	Coverage Δ
ci	83.83% <ø> (+<0.01%)	⬆️

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