feat: add git worktree session support with improved UI

Implement comprehensive worktree session support allowing users to spawn sessions in temporary git worktrees. Includes backend worktree management, full-stack integration, and refined UI for session type selection.

Backend:
- Add worktree creation/removal utilities with branch management
- Track worktree metadata (basePath, branch, name, path) in session metadata
- Automatic cleanup of worktrees when sessions fail or exit
- Enhanced error handling with stderr tail logging

UI improvements:
- Redesign session type toggle with improved alignment and spacing
- Move worktree description inline with label for cleaner layout
- Add branch name input field that appears when worktree mode selected
- Auto-focus on worktree input when switching modes
- Reduce gap between radio options from gap-3 to gap-1.5
- Update descriptive text and placeholders for clarity

Integration:
- Thread worktree parameters through API client, RPC handlers, and daemon
- Add worktreeEnv utility to read worktree info from environment
- Update session spawning to support both simple and worktree modes

cli/src/daemon/controlServer.ts

@@ -108,7 +108,9 @@ export function startDaemonControlServer({
       schema: {
         body: z.object({
           directory: z.string(),
-          sessionId: z.string().optional()
+          sessionId: z.string().optional(),
+          sessionType: z.enum(['simple', 'worktree']).optional(),
+          worktreeName: z.string().optional()
         }),
         response: {
           200: z.object({
@@ -129,10 +131,10 @@ export function startDaemonControlServer({
         }
       }
     }, async (request, reply) => {
-      const { directory, sessionId } = request.body;
+      const { directory, sessionId, sessionType, worktreeName } = request.body;
 
       logger.debug(`[CONTROL SERVER] Spawn session request: dir=${directory}, sessionId=${sessionId || 'new'}`);
-      const result = await spawnSession({ directory, sessionId });
+      const result = await spawnSession({ directory, sessionId, sessionType, worktreeName });
 
       switch (result.type) {
         case 'success':
@@ -208,4 +210,4 @@ export function startDaemonControlServer({
       });
     });
   });
-}
+}