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/pyproject.toml

@@ -1,27 +1,27 @@
 [project]
-name = "castle-cli"
+name = "wildpc-cli"
 version = "0.1.0"
-description = "Castle platform CLI - manage projects, services, and infrastructure"
+description = "Wild PC platform CLI - manage projects, services, and infrastructure"
 requires-python = ">=3.11"
 dependencies = [
     "pyyaml>=6.0.0",
     "jinja2>=3.1.0",
     "pydantic>=2.0.0",
-    "castle-core",
+    "wildpc-core",
 ]
 
 [tool.uv.sources]
-castle-core = { workspace = true }
+wildpc-core = { workspace = true }
 
 [project.scripts]
-castle = "castle_cli.main:main"
+wildpc = "wildpc_cli.main:main"
 
 [build-system]
 requires = ["hatchling"]
 build-backend = "hatchling.build"
 
 [tool.hatch.build.targets.wheel]
-packages = ["src/castle_cli"]
+packages = ["src/wildpc_cli"]
 
 [dependency-groups]
 dev = [