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.md

@@ -1,20 +1,21 @@
-# working-copies
-dir: working-copies
+# openspec/changes/working-copies
+dir: openspec/changes/working-copies
 
-index: working-copies/.pi-map.index.md
+index: openspec/changes/working-copies/.pi-map.index.md
 
 ## 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.
 ## files
+- .openspec.yaml | Defines metadata for a completed project named "working-copies" with timeline tracking
 - design.md | Design document for implementing workspace-based tool instances that replace direct repository mounting with isolated git working copies | dep: FastAPI, SQLAlchemy, Alembic, Docker Compose, Git, React/TypeScript, asyncio subprocess
 - explore.md | Design document proposing "Working Copies" (named "Workspace") as persistent writable clones of repositories to replace direct repo mounting/cloning in tool instances | dep: GitRepository, ToolInstance, Project, User, database, compose generation, filesystem mount system
 - proposal.md | Proposes a new "Workspace" entity to replace the confusing mount/clone mode dichotomy for tool instances, enabling persistent writable repository clones that multiple tools can share.
 - spec.md | Technical specification for implementing persistent workspace-based tool instances that replace mount/clone modes with explicit Git repository workspaces | dep: Git, PostgreSQL, REST API, React/TypeScript frontend, Docker containers, Python backend
-- tasks.md | A project task breakdown document defining a phased implementation plan for adding workspace-based tool instances to a full-stack application, including backend foundation, backend integration, frontend core, and frontend integration PRs with detailed tasks, acceptance criteria, and verification steps. | dep: Alembic, FastAPI, SQLAlchemy, React, TypeScript, Git, Docker Compose, pytest, ruff, ESLint, npm
+- tasks.md | Project task tracking document for implementing workspace-based tool instances across backend and frontend in a multi-PR phased approach | dep: Alembic, FastAPI, SQLAlchemy, React, TypeScript, pytest, ruff, ESLint, Git, Docker Compose
 ## arch
-Design-driven documentation package using phased specification approach (exploration → proposal → design → spec → tasks) to transition from a dual-mode (mount/clone) architecture to a unified workspace entity model with full-stack implementation planning.
+Document-driven design process using layered specification documents (exploration → proposal → design → spec → tasks) with YAML metadata tracking, following a phased multi-PR implementation strategy across backend and frontend systems.
 ## tags
-workspace, tool, instances, git, design, replace, document, repository
+workspace, tool, instances, git, design, replace, project, working
 ## symbols
 -
 ## workflows