feat: complete working-copies workspace-first cleanup

- Remove clone_mode/branch/new_branch from frontend create session flow.
- Add workspace picker to CreateSessionForm; auto-create default workspace when repo selected.
- Fix tool-starter.tsx and use-start-tool.ts createInstance signatures after API change.
- Remove clone mode badge from SessionCard.
- Delete stale backend unit tests referencing removed clone_mode schema fields.
- Update OpenSpec working-copies tasks and mark change completed.
- Regenerate project maps.

Quality gates: npm run typecheck, npm run lint, npm test -- --run (82 passed),
python3 -m py_compile on changed backend files.

openspec/changes/working-copies/.pi-map.index.md

@@ -1,22 +1,23 @@
-# working-copies (index)
-dir: working-copies
+# openspec/changes/working-copies (index)
+dir: openspec/changes/working-copies
 
 ## role
-This package contains design documents and implementation planning for a workspace-based repository access system that replaces direct repository mounting/cloning with isolated, persistent, writable git working copies shared across tool instances.
+Design and specification package for replacing direct repository mounting/cloning with persistent, shared Git working copy workspaces in tool instances.
 ## parent
-index: ./.pi-map.index.md
-map: ./.pi-map.md
+index: openspec/changes/.pi-map.index.md
+map: openspec/changes/.pi-map.md
 ## children
 -
 ## files
+- .openspec.yaml
 - design.md
 - explore.md
 - proposal.md
 - spec.md
 - tasks.md
 ## links
-index: working-copies/.pi-map.index.md
-map: working-copies/.pi-map.md
+index: openspec/changes/working-copies/.pi-map.index.md
+map: openspec/changes/working-copies/.pi-map.md
 ## workflows
 -
 ## dirty