Rename Castle -> Wild PC across the repo

Repo-side rename only (Phases 1-3 of the migration plan); the live box
(~/.castle, systemd units, /data/castle, domains) is a separate cutover.

- Slug `castle` -> `wildpc`: CLI command, module names (wildpc_core/cli/api),
  dist names, entry point `wildpc = wildpc_cli.main:main`.
- Identifiers: CastleConfig/NATSClient/DirError/MDNS -> Wildpc*.
- Env/constants: CASTLE_* -> WILDPC_*; ~/.castle -> ~/.wildpc, castle.yaml ->
  wildpc.yaml, /data/castle -> /data/wildpc.
- Systemd UNIT_PREFIX castle- -> wildpc-; own programs castle-api/gateway/etc.
- Display prose "Castle" -> "Wild PC" in docs, agent-guide files, README, frontend.
- Package dirs and bootstrap yaml renamed via git mv; lockfiles regenerated;
  redundant nested uv.lock files dropped (workspace root lock is authoritative).

Tests: core 273, cli 47, wildpc-api 120 all pass. Frontend type-checks + builds.
Fixed a stale test fixture (secret_env_path kind arg) broken pre-rename.

cli/tests/conftest.py

@@ -1,4 +1,4 @@
-"""Shared fixtures for castle CLI tests."""
+"""Shared fixtures for wildpc CLI tests."""
 
 from __future__ import annotations
 
@@ -51,11 +51,11 @@ def _store_for(spec: dict) -> str:
     ]
 
 
-def _write_castle_config(root: Path, config: dict) -> None:
-    """Scatter a nested castle config dict into the on-disk layout: castle.yaml globals,
+def _write_wildpc_config(root: Path, config: dict) -> None:
+    """Scatter a nested wildpc config dict into the on-disk layout: wildpc.yaml globals,
     programs/<name>.yaml, and deployments/<kind>/<name>.yaml (fields modernized)."""
     globals_data = {k: v for k, v in config.items() if k in ("gateway", "repo")}
-    (root / "castle.yaml").write_text(yaml.dump(globals_data, default_flow_style=False))
+    (root / "wildpc.yaml").write_text(yaml.dump(globals_data, default_flow_style=False))
     programs = config.get("programs") or {}
     if programs:
         (root / "programs").mkdir(parents=True, exist_ok=True)
@@ -70,8 +70,8 @@ def _write_castle_config(root: Path, config: dict) -> None:
 
 
 @pytest.fixture
-def castle_root(tmp_path: Path) -> Generator[Path, None, None]:
-    """Create a temporary castle root with directory-per-resource config."""
+def wildpc_root(tmp_path: Path) -> Generator[Path, None, None]:
+    """Create a temporary wildpc root with directory-per-resource config."""
     config = {
         "gateway": {"port": 18000},
         "programs": {
@@ -129,7 +129,7 @@ def castle_root(tmp_path: Path) -> Generator[Path, None, None]:
             },
         },
     }
-    _write_castle_config(tmp_path, config)
+    _write_wildpc_config(tmp_path, config)
 
     # Create project directories
     svc_dir = tmp_path / "test-svc"
@@ -143,9 +143,9 @@ def castle_root(tmp_path: Path) -> Generator[Path, None, None]:
 
 
 @pytest.fixture
-def castle_home(tmp_path: Path) -> Generator[Path, None, None]:
-    """Create a temporary ~/.castle directory."""
-    home = tmp_path / ".castle"
+def wildpc_home(tmp_path: Path) -> Generator[Path, None, None]:
+    """Create a temporary ~/.wildpc directory."""
+    home = tmp_path / ".wildpc"
     home.mkdir()
     (home / "generated").mkdir()
     (home / "secrets").mkdir()