feat(review): custom base branch for code review (#599) (#602)

Adds a searchable base-branch picker to the code review UI so reviewers
can compare against any branch, not just the auto-detected default.

Key changes:
- Base-branch picker (Radix Popover + search, local/remote groups)
- Diff-type picker (Radix DropdownMenu + info tooltips)
- Worktree picker (Radix Popover + search)
- getDefaultBranch prefers upstream ref (origin/main) for fresher diffs
- listBranches populates GitContext.availableBranches
- resolveBaseBranch trusts caller verbatim (no silent rewrites)
- --end-of-options hardens git argv against flag-injection via base refs
- Branch diff / PR Diff always available (removed hide-on-default guard)
- merge-base agent prompt runs git itself instead of inlining the patch
- Agent jobs snapshot diff context at launch for honest "Copy All"
- Feedback export includes diff mode + base header for agent context
- Round-trip base through /api/diff so refresh preserves the selection
- selectedBase / committedBase split prevents file-content race
- Optimistic picker reverts on switch failure
- DiffViewer remounts on mode switch to invalidate stale file content
- Worktree switch preserves active diff mode
- Pi parity: initialBase, currentBase, agent diffContext, vendor.sh
- Tooltip wide mode, TooltipProvider mounted, keyboard/touch fixes
- GPT-5.5 added to Codex model picker
- CLAUDE.md API table updated

Closes #599

For provenance purposes, this PR was AI assisted.

packages/review-editor/package.json

@@ -12,6 +12,9 @@
     "@plannotator/ui": "workspace:*",
     "@radix-ui/react-checkbox": "^1.3.3",
     "@radix-ui/react-collapsible": "^1.1.12",
+    "@radix-ui/react-dialog": "^1.1.15",
+    "@radix-ui/react-dropdown-menu": "^2.1.15",
+    "@radix-ui/react-popover": "^1.1.15",
     "@radix-ui/react-tooltip": "^1.2.8",
     "highlight.js": "^11.11.1",
     "motion": "^12.38.0",