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.

wildpc-api/CLAUDE.md

@@ -0,0 +1,31 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working
+with code in this repository.
+
+## Overview
+
+wildpc-api is a FastAPI service. Wild PC API.
+
+## Commands
+
+```bash
+uv sync                     # Install dependencies
+uv run wildpc-api                 # Run service (port 9020)
+uv run pytest tests/ -v     # Run tests
+uv run ruff check .         # Lint
+uv run ruff format .        # Format
+```
+
+## Architecture
+
+- `src/wildpc_api/config.py` — Settings via pydantic-settings, env prefix `WILDPC_API_`
+- `src/wildpc_api/main.py` — FastAPI app, lifespan, health endpoint
+- `tests/` — pytest with TestClient fixtures
+
+## Configuration
+
+Environment variables with `WILDPC_API_` prefix:
+- `WILDPC_API_DATA_DIR` — Data directory (default: ./data)
+- `WILDPC_API_HOST` — Bind host (default: 0.0.0.0)
+- `WILDPC_API_PORT` — Port (default: 9020)