feat(composer): recall sent messages with the arrow keys

[luoxuanzao]

Summary

• With the message input empty, ArrowUp now walks back through the messages
  you sent in the current conversation; ArrowDown walks forward again and
  clears the input past the newest message, so an earlier prompt can be
  recalled, edited, or resent without scrolling the transcript.
• History is read from the messages already in the pane — a new
  PromptHistoryController picks user messages, skips interrupts and rebuilt
  context, and recalls the text the bubble shows — so it survives restarts
  without extra storage.
• Browsing drops out when the recalled text is edited, the conversation is
  switched, or the message is sent; IME compositions, modifier-held arrows,
  an armed # instruction mode, and visible composer dropdowns keep their
  current behavior.
• Documented under [Unreleased] in CHANGELOG.md (Added).

Verification

• npm run typecheck
• npm run lint
• npm run test (167 suites, 3570 tests; 15 of them new for the controller)
• npm run build
• npm run release:check
• npm run audit:prod
• Tested affected qodercli behavior against a real CLI when applicable —
  no CLI behavior is involved; the build was deployed to a local vault and
  exercised in Obsidian instead.

Safety

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