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.

core/tests/test_audit.py

@@ -1,10 +1,10 @@
-"""Tests for the consumption audit (core/src/castle_core/audit.py)."""
+"""Tests for the consumption audit (core/src/wildpc_core/audit.py)."""
 
 from __future__ import annotations
 
-import castle_core.config as C
-from castle_core import audit
-from castle_core.manifest import SystemdDeployment
+import wildpc_core.config as C
+from wildpc_core import audit
+from wildpc_core.manifest import SystemdDeployment
 
 
 def _svc(
@@ -33,8 +33,8 @@ def _svc(
     return SystemdDeployment.model_validate(spec)
 
 
-def _cfg(deployments: dict) -> C.CastleConfig:
-    return C.CastleConfig(
+def _cfg(deployments: dict) -> C.WildpcConfig:
+    return C.WildpcConfig(
         root=None,
         gateway=C.GatewayConfig(port=9000),
         repo=None,
@@ -43,7 +43,7 @@ def _cfg(deployments: dict) -> C.CastleConfig:
     )
 
 
-def _pairs(cfg: C.CastleConfig) -> set[tuple[str, str]]:
+def _pairs(cfg: C.WildpcConfig) -> set[tuple[str, str]]:
     return {(s.consumer, s.provider) for s in audit.suggest_consumption(cfg)}
 
 
@@ -55,7 +55,7 @@ def test_split_host_port_pair_is_suggested() -> None:
             "api": _svc(
                 "api",
                 http=9020,
-                env={"CASTLE_API_MQTT_HOST": "localhost", "CASTLE_API_MQTT_PORT": "1883"},
+                env={"WILDPC_API_MQTT_HOST": "localhost", "WILDPC_API_MQTT_PORT": "1883"},
             ),
         }
     )