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/utils/worktreeEnv.ts

@@ -0,0 +1,26 @@
+import type { WorktreeInfo } from '@/daemon/worktree';
+
+export function readWorktreeEnv(): WorktreeInfo | null {
+  const basePath = process.env.HAPI_WORKTREE_BASE_PATH?.trim();
+  const branch = process.env.HAPI_WORKTREE_BRANCH?.trim();
+  const name = process.env.HAPI_WORKTREE_NAME?.trim();
+  const worktreePath = process.env.HAPI_WORKTREE_PATH?.trim();
+  const createdAtRaw = process.env.HAPI_WORKTREE_CREATED_AT?.trim();
+
+  if (!basePath || !branch || !name || !worktreePath || !createdAtRaw) {
+    return null;
+  }
+
+  const createdAt = Number(createdAtRaw);
+  if (!Number.isFinite(createdAt)) {
+    return null;
+  }
+
+  return {
+    basePath,
+    branch,
+    name,
+    worktreePath,
+    createdAt
+  };
+}