fix(bootstrap): create local .venv with symlinks=True

Without symlinks=True, mise/asdf shared-library Python builds on macOS
default venv to copy mode. The copied python3 binary still references
@executable_path/../lib/libpython3.X.dylib in its load command, but the
dylib is never copied into .venv/lib — so any import in the new venv
(starting with ensurepip) aborts with SIGABRT.

Reproduces with mise's cpython 3.13.9 build:

    [bootstrap] Creating local virtualenv at .../.venv
    [bootstrap] ERROR: Command '[".../.venv/bin/python3.13", "-m",
      "ensurepip", "--upgrade", "--default-pip"]' died with
      <Signals.SIGABRT: 6>.

Symlinking the interpreter keeps @executable_path resolving back to the
original install where libpython lives. uv-managed Pythons already
symlink by default; mise's do not.

bootstrap.py

@@ -179,7 +179,13 @@ def ensure_python_has_webui_deps(python_exe: str, agent_dir: Path | None = None)
     )
     if not venv_python.exists():
         info(f"Creating local virtualenv at {venv_dir}")
-        venv.EnvBuilder(with_pip=True).create(venv_dir)
+        # symlinks=True: some Python builds (notably mise/asdf shared-library
+        # installs on macOS) default venv to copy mode. The copied binary still
+        # uses @executable_path/../lib/libpython3.X.dylib for its load command,
+        # so the venv binary aborts with SIGABRT on first import because the
+        # dylib never gets copied into .venv/lib. Symlinking the interpreter
+        # keeps @executable_path resolving back to the original install.
+        venv.EnvBuilder(with_pip=True, symlinks=True).create(venv_dir)
 
     info("Installing WebUI dependencies into local virtualenv")
     subprocess.run(