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_graph_repos.py

@@ -0,0 +1,71 @@
+"""Tests for the /graph diagnostic and /repos (repo-scoped sync) endpoints."""
+
+import os
+import subprocess
+from pathlib import Path
+
+from fastapi.testclient import TestClient
+
+_ENV = {
+    "GIT_AUTHOR_NAME": "t",
+    "GIT_AUTHOR_EMAIL": "t@t",
+    "GIT_COMMITTER_NAME": "t",
+    "GIT_COMMITTER_EMAIL": "t@t",
+    "GIT_CONFIG_GLOBAL": "/dev/null",
+    "GIT_CONFIG_SYSTEM": "/dev/null",
+}
+
+
+def _git(cwd: Path, *args: str) -> None:
+    subprocess.run(
+        ["git", "-C", str(cwd), *args],
+        check=True,
+        capture_output=True,
+        text=True,
+        env={**os.environ, **_ENV},
+    )
+
+
+def _commit(cwd: Path, fname: str) -> None:
+    (cwd / fname).write_text(fname)
+    _git(cwd, "add", fname)
+    _git(cwd, "commit", "-m", f"add {fname}")
+
+
+def _setup(work: Path) -> None:
+    upstream = work.parent / f"{work.name}-upstream"
+    upstream.mkdir()
+    _git(upstream, "init", "-q", "-b", "main")
+    _commit(upstream, "a.txt")
+    _git(work.parent, "clone", "-q", str(upstream), str(work))
+
+
+class TestGraph:
+    def test_graph_shape(self, client: TestClient) -> None:
+        resp = client.get("/graph")
+        assert resp.status_code == 200
+        body = resp.json()
+        assert {"repos", "nodes", "edges"} <= body.keys()
+        # every node carries the derived predicates
+        assert all("functional" in n for n in body["nodes"])
+
+
+class TestRepos:
+    def test_list_and_sync(self, client: TestClient, wildpc_root: Path) -> None:
+        _setup(wildpc_root / "wired-in")  # program `wired-in` source → <root>/wired-in
+        _commit(wildpc_root / "wired-in-upstream", "b.txt")  # advance remote
+
+        repos = {r["key"]: r for r in client.get("/repos").json()}
+        assert "wired-in" in repos
+        assert "wired-in" in repos["wired-in"]["programs"]
+
+        gitinfo = client.get("/repos/wired-in/git").json()
+        assert gitinfo["is_repo"] is True and gitinfo["behind"] == 1
+
+        synced = client.post("/repos/wired-in/sync").json()
+        assert synced["pulled"] is True and "wired-in" in synced["deployments"]
+        assert (wildpc_root / "wired-in" / "b.txt").exists()
+
+    def test_unknown_repo_404(self, client: TestClient) -> None:
+        assert client.get("/repos/nope/git").status_code == 404
+        assert client.post("/repos/nope/sync").status_code == 404