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/test_mesh.py

@@ -1,4 +1,4 @@
-"""Tests for the castle mesh command (API calls mocked)."""
+"""Tests for the wildpc mesh command (API calls mocked)."""
 
 from __future__ import annotations
 
@@ -6,7 +6,7 @@ import urllib.error
 from argparse import Namespace
 from unittest.mock import patch
 
-from castle_cli.commands.mesh import run_mesh
+from wildpc_cli.commands.mesh import run_mesh
 
 
 class TestMeshCommand:
@@ -15,7 +15,7 @@ class TestMeshCommand:
             "enabled": True, "connected": True, "nats_url": "tls://x:4222",
             "peer_count": 1, "peers": ["primer"],
         }
-        with patch("castle_cli.commands.mesh._get", return_value=data):
+        with patch("wildpc_cli.commands.mesh._get", return_value=data):
             rc = run_mesh(Namespace(mesh_command="status"))
         assert rc == 0
         out = capsys.readouterr().out  # type: ignore[attr-defined]
@@ -28,7 +28,7 @@ class TestMeshCommand:
             {"hostname": "primer", "online": True, "is_stale": False,
              "deployed_count": 3, "is_local": False},
         ]
-        with patch("castle_cli.commands.mesh._get", return_value=data):
+        with patch("wildpc_cli.commands.mesh._get", return_value=data):
             rc = run_mesh(Namespace(mesh_command="nodes"))
         assert rc == 0
         out = capsys.readouterr().out  # type: ignore[attr-defined]
@@ -36,7 +36,7 @@ class TestMeshCommand:
 
     def test_config_list(self, capsys: object) -> None:
         data = {"role": "authority", "keys": ["fleet/motd"]}
-        with patch("castle_cli.commands.mesh._get", return_value=data):
+        with patch("wildpc_cli.commands.mesh._get", return_value=data):
             rc = run_mesh(
                 Namespace(mesh_command="config", mesh_config_command="list")
             )
@@ -45,7 +45,7 @@ class TestMeshCommand:
 
     def test_config_set_calls_put(self) -> None:
         with patch(
-            "castle_cli.commands.mesh._put", return_value={"ok": True}
+            "wildpc_cli.commands.mesh._put", return_value={"ok": True}
         ) as put:
             rc = run_mesh(
                 Namespace(
@@ -60,7 +60,7 @@ class TestMeshCommand:
 
     def test_api_unreachable_returns_1(self, capsys: object) -> None:
         with patch(
-            "castle_cli.commands.mesh._get",
+            "wildpc_cli.commands.mesh._get",
             side_effect=urllib.error.URLError("refused"),
         ):
             rc = run_mesh(Namespace(mesh_command="status"))