feat: conversation history frontend (#19)

* feat: conversation history frontend — milestone 1

Add HistoryPanel, ConversationItem, SwitchConfirmation components,
useConversationHistory hook, and history types. Integrate history
entry point into AskBarView and ConversationView. Wire up full
test coverage and update mocks/vitest config to support new
Tauri command surface (list_conversations, load_conversation,
delete_conversation, save_conversation, generate_title).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Logan Nguyen <lg.131.dev@gmail.com>

* fix: three bugs in conversation history handlers

- handleDeleteConversation now calls reset() to clear messages when the
  active conversation is deleted, preventing stale chat state in ask-bar mode
- all async history handlers (handleSave, handleLoadConversation,
  handleSaveAndLoad, handleDeleteConversation) wrapped in try/catch to
  prevent unhandled promise rejections from crashing the UI
- HistoryPanel.handleDelete made async with snapshot-based rollback: if
  onDeleteConversation rejects, the item is restored to its original sort
  position in the list

233 tests, 100% coverage, validate-build clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Logan Nguyen <lg.131.dev@gmail.com>

* chore: raise Vite chunkSizeWarningLimit to 900 kB

Bundle grew to 833 kB after adding streamdown + history panel deps.
Raise the threshold to suppress the spurious build warning.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Logan Nguyen <lg.131.dev@gmail.com>

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Signed-off-by: Logan Nguyen <lg.131.dev@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: quiet-node