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/checkout-git.test.ts

@@ -17,6 +17,7 @@ import {
   MergeFromBaseConflictError,
   NotGitRepoError,
   pushCurrentBranch,
+  resolveRepositoryDefaultBranch,
 } from "./checkout-git.js";
 import { createWorktree } from "./worktree.js";
 import { getPaseoWorktreeMetadataPath } from "./worktree-metadata.js";
@@ -707,6 +708,17 @@ describe("checkout git utilities", () => {
     expect(baseDiff.diff).not.toContain("file.txt");
   });
 
+  it("resolves the repository default branch from origin HEAD", async () => {
+    execSync("git checkout -b develop", { cwd: repoDir });
+    execSync("git checkout main", { cwd: repoDir });
+    execSync("git remote add origin https://github.com/acme/repo.git", { cwd: repoDir });
+    execSync("git update-ref refs/remotes/origin/main refs/heads/main", { cwd: repoDir });
+    execSync("git update-ref refs/remotes/origin/develop refs/heads/develop", { cwd: repoDir });
+    execSync("git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main", { cwd: repoDir });
+
+    await expect(resolveRepositoryDefaultBranch(repoDir)).resolves.toBe("main");
+  });
+
   it("merges to stored baseRefName when baseRef is not provided", async () => {
     // Create a non-default base branch with a unique commit.
     execSync("git checkout -b develop", { cwd: repoDir });