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/tests/test_nats_integration.py

@@ -0,0 +1,117 @@
+"""Integration tests for WildpcNATSClient against a real NATS/JetStream broker.
+
+Exercises the runtime the unit tests can't: connect, KV publish, peer discovery
+via watch, presence, graceful-offline, and shared-config. Requires docker (the
+`nats_url` fixture); skipped otherwise.
+"""
+
+from __future__ import annotations
+
+import asyncio
+
+import pytest
+from wildpc_core.registry import Deployment, NodeConfig, NodeRegistry
+
+import wildpc_api.nats_client as ncmod
+from wildpc_api.mesh import mesh_state
+from wildpc_api.nats_client import WildpcNATSClient
+
+
+@pytest.fixture(autouse=True)
+def _isolate(monkeypatch):
+    """Stub the gateway-regen side effect (so tests never touch the host's real
+    Caddyfile) and clear the shared mesh_state singleton around each test."""
+
+    async def _stub(*_a, **_k):
+        return False
+
+    monkeypatch.setattr(ncmod, "refresh_remote_routes", _stub)
+    mesh_state._nodes.clear()
+    yield
+    mesh_state._nodes.clear()
+
+
+def _reg(host: str, deployed=None, role: str = "follower") -> NodeRegistry:
+    return NodeRegistry(
+        node=NodeConfig(hostname=host, role=role), deployed=deployed or {}
+    )
+
+
+def _widget_reg(host: str) -> NodeRegistry:
+    w = Deployment(
+        manager="systemd", launcher="python", run_cmd=[], name="widget",
+        kind="service", port=9099, subdomain="widget",
+    )
+    return _reg(host, {NodeRegistry.key("service", "widget"): w})
+
+
+def test_publish_peer_discovery_and_offline(nats_url: str) -> None:
+    async def run() -> None:
+        a = WildpcNATSClient("node-a", _reg("node-a"), servers=nats_url)
+        b = WildpcNATSClient("node-b", _widget_reg("node-b"), servers=nats_url)
+        await a.start()
+        await b.start()
+        await asyncio.sleep(1.0)  # let watches propagate
+
+        nodes = mesh_state.all_nodes(include_stale=True)
+        assert "node-b" in nodes, "node-a should discover node-b via the KV watch"
+        assert nodes["node-b"].registry.get("service", "widget") is not None
+
+        # Graceful stop deletes b's key -> the DELETE watch marks it offline.
+        await b.stop()
+        await asyncio.sleep(1.0)
+        nb = mesh_state.get_node("node-b")
+        assert nb is None or not nb.online
+
+        await a.stop()
+
+    asyncio.run(run())
+
+
+def test_presence_key_written(nats_url: str) -> None:
+    async def run() -> None:
+        c = WildpcNATSClient("solo", _reg("solo"), servers=nats_url)
+        await c.start()
+        keys = await c._presence_kv.keys()
+        assert "solo" in keys
+        await c.stop()
+
+    asyncio.run(run())
+
+
+def test_shared_config_authority_write_read(nats_url: str) -> None:
+    async def run() -> None:
+        auth = WildpcNATSClient("auth", _reg("auth", role="authority"), servers=nats_url)
+        await auth.start()
+        await auth.put_shared_config("fleet/motd", "hello")
+        assert await auth.get_shared_config("fleet/motd") == "hello"
+        assert "fleet/motd" in await auth.list_shared_config()
+        await auth.stop()
+
+    asyncio.run(run())
+
+
+def test_secrets_never_on_the_wire(nats_url: str) -> None:
+    """The registry a peer receives must carry no env/run_cmd."""
+    async def run() -> None:
+        secretful = Deployment(
+            manager="systemd", launcher="python",
+            run_cmd=["uv", "run", "svc"], env={"API_KEY": "s3cr3t"},
+            name="svc", kind="service", port=9001, subdomain="svc",
+        )
+        a = WildpcNATSClient("wa", _reg("wa"), servers=nats_url)
+        b = WildpcNATSClient(
+            "wb", _reg("wb", {NodeRegistry.key("service", "svc"): secretful}),
+            servers=nats_url,
+        )
+        await a.start()
+        await b.start()
+        await asyncio.sleep(1.0)
+        svc = mesh_state.get_node("wb").registry.get("service", "svc")
+        assert svc is not None
+        assert not svc.env, "env must not cross the wire"
+        assert not svc.run_cmd, "run_cmd must not cross the wire"
+        await a.stop()
+        await b.stop()
+
+    asyncio.run(run())