feat: Auto-branch initiative system with per-project default branches

Planning tasks (research, discuss, plan, detail, refine) now run on
the project's defaultBranch instead of hardcoded 'main'. Execution
tasks (execute, verify, merge, review) auto-generate an initiative
branch (cw/<slug>) on first dispatch. Branch configuration removed
from initiative creation — it's now fully automatic.

- Add PLANNING_CATEGORIES/EXECUTION_CATEGORIES to branch-naming
- Dispatch manager splits logic by task category
- ProcessManager uses per-project defaultBranch fallback
- Phase dispatch uses project.defaultBranch for ensureBranch base
- Remove mergeTarget from createInitiative input
- Rename updateInitiativeMergeConfig → updateInitiativeConfig
- Add defaultBranch field to registerProject + UI
- Rename mergeTarget → branch across all frontend components

src/agent/file-io.test.ts

@@ -49,7 +49,7 @@ describe('writeInputFiles', () => {
       name: 'Test Initiative',
       status: 'active',
       mergeRequiresApproval: true,
-      mergeTarget: 'main',
+      branch: 'cw/test-initiative',
       executionMode: 'review_per_phase',
       createdAt: new Date('2026-01-01'),
       updatedAt: new Date('2026-01-02'),

src/agent/file-io.ts

@@ -125,7 +125,7 @@ export function writeInputFiles(options: WriteInputFilesOptions): void {
         name: ini.name,
         status: ini.status,
         mergeRequiresApproval: ini.mergeRequiresApproval,
-        mergeTarget: ini.mergeTarget,
+        branch: ini.branch,
       },
       '',
     );

src/agent/manager.ts

@@ -222,7 +222,7 @@ export class MultiProviderAgentManager implements AgentManager {
     let agentCwd: string;
     if (initiativeId) {
       log.debug({ alias, initiativeId, baseBranch, branchName }, 'creating initiative-based worktrees');
-      agentCwd = await this.processManager.createProjectWorktrees(alias, initiativeId, baseBranch ?? 'main', branchName);
+      agentCwd = await this.processManager.createProjectWorktrees(alias, initiativeId, baseBranch, branchName);
 
       // Log projects linked to the initiative
       const projects = await this.projectRepository.findProjectsByInitiativeId(initiativeId);

src/agent/process-manager.ts

@@ -54,7 +54,7 @@ export class ProcessManager {
   async createProjectWorktrees(
     alias: string,
     initiativeId: string,
-    baseBranch: string = 'main',
+    baseBranch?: string,
     branchName?: string,
   ): Promise<string> {
     const projects = await this.projectRepository.findProjectsByInitiativeId(initiativeId);
@@ -78,7 +78,8 @@ export class ProcessManager {
     for (const project of projects) {
       const clonePath = await ensureProjectClone(project, this.workspaceRoot);
       const worktreeManager = new SimpleGitWorktreeManager(clonePath, undefined, agentWorkdir);
-      const worktree = await worktreeManager.create(project.name, branchName ?? `agent/${alias}`, baseBranch);
+      const effectiveBaseBranch = baseBranch ?? project.defaultBranch;
+      const worktree = await worktreeManager.create(project.name, branchName ?? `agent/${alias}`, effectiveBaseBranch);
       const worktreePath = worktree.path;
       const pathExists = existsSync(worktreePath);