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/agent/runners/runAgentSession.ts

@@ -20,6 +20,7 @@ import { initialMachineMetadata } from '@/daemon/run';
 import { startHappyServer } from '@/claude/utils/startHappyServer';
 import { getHappyCliCommand } from '@/utils/spawnHappyCLI';
 import { registerKillSessionHandler } from '@/claude/registerKillSessionHandler';
+import { readWorktreeEnv } from '@/utils/worktreeEnv';
 
 function emitReadyIfIdle(props: {
     queueSize: () => number;
@@ -56,6 +57,7 @@ export async function runAgentSession(opts: {
         controlledByUser: false
     };
 
+    const worktreeInfo = readWorktreeEnv();
     const metadata: Metadata = {
         path: process.cwd(),
         host: os.hostname(),
@@ -71,7 +73,8 @@ export async function runAgentSession(opts: {
         startedBy: opts.startedBy || 'terminal',
         lifecycleState: 'running',
         lifecycleStateSince: Date.now(),
-        flavor: opts.agentType
+        flavor: opts.agentType,
+        worktree: worktreeInfo ?? undefined
     };
 
     const response = await api.getOrCreateSession({ tag: sessionTag, metadata, state });