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.

app/vite.config.ts

@@ -4,8 +4,8 @@ import { defineConfig } from "vite"
 import react from "@vitejs/plugin-react"
 
 export default defineConfig({
-  // Castle sets VITE_BASE to the gateway serve prefix at build time so absolute
-  // asset URLs resolve at the subpath (castle-app is the root app → "/").
+  // Wild PC sets VITE_BASE to the gateway serve prefix at build time so absolute
+  // asset URLs resolve at the subpath (wildpc-app is the root app → "/").
   base: process.env.VITE_BASE ?? "/",
   plugins: [react(), tailwindcss()],
   resolve: {