feat: show file change summary bar (#950)

* feat: add FileChangeSummary component for multi-file diff preview in ToolPart

Provides an aggregated diff card for apply_patch and multi-edit tools,
showing per-file stats with click-to-expand diff view.

* feat: add PendingChangesBar above chat input with collapse/expand and file opening

- Collapsed/expanded toggle with aggregate +N -N stats (green/red)
- Relative path display, chat-column alignment with ChatInput
- Click file to open in diff viewer (web/desktop) or editor (VS Code)
- Support edit/multiedit/apply_patch/write tool metadata extraction
- Add PendingChangesBar to main chat view (ChatContainer)

* feat: dual-mode ChangedFilesBar — Git diff state vs latest AI turn

Git mode: reads git status from useGitStore (status.files + diffStats),
auto-clears on commit/restore. Shows 'N files changed in workspace'.

Non-Git mode: latest assistant turn only (no accumulation), clears on new
user message or manual dismiss. Shows 'AI updated N files in the last reply'.

Both modes: dismiss button with signature-based tracking.
Add pendingChangesBarDismissed state to session-ui-store, cleared on sendMessage.

* fix: address code review issues in ChangedFilesBar

- Gate non-git mode on streaming state to prevent flicker during AI turns
- Return null when isGitRepo is unknown (loading state)
- Add group/row class for reject button visibility in FileChangeSummary
- Use per-session Map for dismiss tracking to prevent cross-session leaks
- Include additions/deletions in dismiss signature for re-edit detection
- Extract shared parsePatchStats/parseCount to fileChangeHelpers

* chore: revert local .opencode/package-lock.json changes from PR

* fix: per-part fallback guard and git-only reject button

- Fix extractChangedFiles to use per-part files.length snapshot instead
  of global guard, preventing file entries from being skipped when
  earlier parts already contributed files
- Hide reject button in FileChangeSummary when not in a git repo,
  preventing silent revert failures

* refactor: remove FileChangeSummary — dead code redundant with ToolPart

FileChangeSummary duplicated diff rendering that ToolPart already
provides (PatchDiff, per-file stats, DiffViewToggle). The only unique
feature was a git revert button, which conflicts with the design
principle of not having accept/reject on file change previews.

Moved parsePatchStats/parseCount back into PendingChangesBar (sole
consumer) and deleted the shared helper module.

* chore: remove stray Tester.txt

* fix: deduplicate Fallback 4 'Diff' placeholder via seen set

* chore: update non-Git mode copy to neutral 'changed in the last reply'

* fix(chat): unify changes row with tasks

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/index.css

@@ -763,6 +763,19 @@ html:not(.dark) .chat-scroll {
   }
 }
 
+/* Status row: collapse optional text when narrow to keep both sides in one line. */
+@container status-row (max-width: 30rem) {
+  .status-row__active-todo {
+    display: none;
+  }
+}
+
+@container status-row (max-width: 24rem) {
+  .status-row__changed-label {
+    display: none;
+  }
+}
+
 /* Animated tabs: collapse labels based on local container width. */
 @container animated-tabs (max-width: 23rem) {
   .animated-tabs__label {