feat: persist concurrent agents slider at project level

Add `default_concurrency` column to the projects table in the registry
database, allowing each project to remember its preferred concurrency
setting (1-5 agents). The value persists across page refreshes and
app restarts.

Backend changes:
- Add `default_concurrency` column to Project model in registry.py
- Add database migration for existing databases (ALTER TABLE)
- Add get/set_project_concurrency() CRUD functions
- Add ProjectSettingsUpdate schema with validation
- Add PATCH /{name}/settings endpoint in projects router
- Include default_concurrency in ProjectSummary/ProjectDetail responses

Frontend changes:
- Add default_concurrency to ProjectSummary TypeScript interface
- Add ProjectSettingsUpdate type and updateProjectSettings API function
- Add useUpdateProjectSettings React Query mutation hook
- Update AgentControl to accept defaultConcurrency prop
- Sync local state when project changes via useEffect
- Debounce slider changes (500ms) before saving to backend
- Pass defaultConcurrency from selectedProjectData in App.tsx

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/commands/review-pr.md

@@ -12,18 +12,43 @@ Pull request(s): $ARGUMENTS
 1. **Retrieve PR Details**
    - Use the GH CLI tool to retrieve the details (descriptions, diffs, comments, feedback, reviews, etc)
 
-2. **Analyze Codebase Impact**
-   - Use 3 deepdive subagents to analyze the impact on the codebase
+2. **Assess PR Complexity**
 
-3. **Vision Alignment Check**
+   After retrieving PR details, assess complexity based on:
+   - Number of files changed
+   - Lines added/removed
+   - Number of contributors/commits
+   - Whether changes touch core/architectural files
+
+   ### Complexity Tiers
+
+   **Simple** (no deep dive agents needed):
+   - ≤5 files changed AND ≤100 lines changed AND single author
+   - Review directly without spawning agents
+
+   **Medium** (1-2 deep dive agents):
+   - 6-15 files changed, OR 100-500 lines, OR 2 contributors
+   - Spawn 1 agent for focused areas, 2 if changes span multiple domains
+
+   **Complex** (up to 3 deep dive agents):
+   - >15 files, OR >500 lines, OR >2 contributors, OR touches core architecture
+   - Spawn up to 3 agents to analyze different aspects (e.g., security, performance, architecture)
+
+3. **Analyze Codebase Impact**
+   - Based on the complexity tier determined above, spawn the appropriate number of deep dive subagents
+   - For Simple PRs: analyze directly without spawning agents
+   - For Medium PRs: spawn 1-2 agents focusing on the most impacted areas
+   - For Complex PRs: spawn up to 3 agents to cover security, performance, and architectural concerns
+
+4. **Vision Alignment Check**
    - Read the project's README.md and CLAUDE.md to understand the application's core purpose
    - Assess whether this PR aligns with the application's intended functionality
    - If the changes deviate significantly from the core vision or add functionality that doesn't serve the application's purpose, note this in the review
    - This is not a blocker, but should be flagged for the reviewer's consideration
 
-4. **Safety Assessment**
+5. **Safety Assessment**
    - Provide a review on whether the PR is safe to merge as-is
    - Provide any feedback in terms of risk level
 
-5. **Improvements**
+6. **Improvements**
    - Propose any improvements in terms of importance and complexity