Simplify workspace creation with inline worktree API

Replace the multi-step new-agent route flow with a single
create_paseo_worktree endpoint that registers the workspace immediately
and creates the git worktree in the background. The sidebar now calls
this endpoint directly and shows a creating spinner inline.

Also auto-resolves the base branch from origin/HEAD when not explicitly
provided, removes the unused Tauri WebSocket transport layer, and
normalizes loopback endpoints to localhost.

Closes #125

packages/server/src/utils/worktree.ts

@@ -668,12 +668,21 @@ export async function deriveWorktreeProjectHash(cwd: string): Promise<string> {
   }
 }
 
-async function getPaseoWorktreesRoot(cwd: string, paseoHome?: string): Promise<string> {
+export async function getPaseoWorktreesRoot(cwd: string, paseoHome?: string): Promise<string> {
   const home = paseoHome ? resolve(paseoHome) : resolvePaseoHome();
   const projectHash = await deriveWorktreeProjectHash(cwd);
   return join(home, "worktrees", projectHash);
 }
 
+export async function computeWorktreePath(
+  cwd: string,
+  slug: string,
+  paseoHome?: string
+): Promise<string> {
+  const worktreesRoot = await getPaseoWorktreesRoot(cwd, paseoHome);
+  return join(worktreesRoot, slug);
+}
+
 function normalizePathForOwnership(input: string): string {
   try {
     return realpathSync(input);