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.

apps/.pi-map.md

@@ -4,10 +4,10 @@ dir: apps
 index: apps/.pi-map.index.md
 
 ## role
-Contains the main application entry points and executable modules for the project.
+Contains the top-level application entry points and executable binaries for the project.
 ## files
 ## arch
-Typically follows a modular architecture where each subdirectory represents a separate deployable application sharing common domain libraries.
+Follows a workspace/monorepo pattern where each subdirectory is a distinct deployable application sharing common libraries.
 ## tags
 -
 ## symbols