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/api/apiMachine.ts

@@ -70,7 +70,7 @@ export class ApiMachineClient {
 
     setRPCHandlers({ spawnSession, stopSession, requestShutdown }: MachineRpcHandlers): void {
         this.rpcHandlerManager.registerHandler('spawn-happy-session', async (params: any) => {
-            const { directory, sessionId, machineId, approvedNewDirectoryCreation, agent, yolo, token } = params || {}
+            const { directory, sessionId, machineId, approvedNewDirectoryCreation, agent, yolo, token, sessionType, worktreeName } = params || {}
 
             if (!directory) {
                 throw new Error('Directory is required')
@@ -83,7 +83,9 @@ export class ApiMachineClient {
                 approvedNewDirectoryCreation,
                 agent,
                 yolo,
-                token
+                token,
+                sessionType,
+                worktreeName
             })
 
             switch (result.type) {