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/src/wildpc_cli/commands/stack.py

@@ -0,0 +1,110 @@
+"""wildpc stack — the stacks lens (toolchains a program's stack needs).
+
+A *stack* (python-fastapi, react-vite, hugo, …) is creation-time guidance that
+also carries the **host toolchains** its programs need to build and run (`uv`,
+`pnpm`, `hugo`, …). This lens makes those dependencies visible and tells you
+whether they're present *where the running service needs them* — the drift a bare
+`which` in your shell misses — with a copyable fix when one is absent.
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+from dataclasses import asdict
+from typing import TYPE_CHECKING
+
+from wildpc_cli.config import load_config
+
+if TYPE_CHECKING:
+    from wildpc_core.stack_status import StackStatus
+
+BOLD = "\033[1m"
+DIM = "\033[2m"
+RESET = "\033[0m"
+GREEN = "\033[92m"
+RED = "\033[91m"
+GREY = "\033[90m"
+CYAN = "\033[96m"
+
+
+def _record(st: StackStatus) -> dict:
+    d = asdict(st)
+    d["in_use"] = st.in_use
+    d["ok"] = st.ok
+    return d
+
+
+def run_stack_list(args: argparse.Namespace) -> int:
+    """List stacks with their toolchain health, program count, and dev verbs."""
+    from wildpc_core.stack_status import all_stack_status
+
+    config = load_config()
+    # Skip per-tool version probes for the list (a subprocess per tool) — keep it snappy.
+    stacks = all_stack_status(config, with_version=False)
+
+    if getattr(args, "json", False):
+        print(json.dumps([_record(s) for s in stacks], indent=2))
+        return 0
+
+    print(f"\n{BOLD}Stacks{RESET}")
+    print("─" * 64)
+    width = max((len(s.name) for s in stacks), default=0)
+    for s in stacks:
+        if not s.tools:
+            dot = f"{GREY}○{RESET}"
+        else:
+            dot = f"{GREEN}●{RESET}" if s.ok else f"{RED}●{RESET}"
+        missing = [t.command for t in s.tools if not t.present]
+        tools = ", ".join(
+            (f"{RED}{t.command}{RESET}" if not t.present else t.command) for t in s.tools
+        )
+        used = (
+            f"{len(s.programs)} program{'s' if len(s.programs) != 1 else ''}"
+            if s.in_use
+            else f"{GREY}unused{RESET}"
+        )
+        tail = f"  {DIM}{used}{RESET}"
+        tools_str = f"  {DIM}tools:{RESET} {tools}" if tools else ""
+        print(f"  {dot} {BOLD}{s.name:<{width}}{RESET}{tools_str}{tail}")
+        if missing:
+            print(f"      {RED}missing:{RESET} {', '.join(missing)}")
+    print()
+    return 0
+
+
+def run_stack_info(args: argparse.Namespace) -> int:
+    """Show one stack: each tool's presence + version + fix, and who uses it."""
+    from wildpc_core.stack_status import stack_status
+
+    config = load_config()
+    name = args.name
+    st = stack_status(config, name)
+    if st is None:
+        from wildpc_core.stacks import available_stacks
+
+        print(f"Error: no stack '{name}'. Known: {', '.join(available_stacks())}")
+        return 1
+
+    if getattr(args, "json", False):
+        print(json.dumps(_record(st), indent=2))
+        return 0
+
+    print(f"\n{BOLD}{st.name}{RESET}")
+    print("─" * 48)
+    if st.verbs:
+        print(f"  {BOLD}verbs{RESET}:    {', '.join(st.verbs)}")
+    print(f"  {BOLD}used by{RESET}:  ", end="")
+    print(", ".join(st.programs) if st.programs else f"{GREY}nothing{RESET}")
+
+    print(f"\n  {BOLD}toolchain{RESET}")
+    if not st.tools:
+        print(f"    {GREY}no host tools required{RESET}")
+    for t in st.tools:
+        mark = f"{GREEN}✓{RESET}" if t.present else f"{RED}✗{RESET}"
+        ver = f"  {DIM}{t.version}{RESET}" if t.version else ""
+        print(f"    {mark} {BOLD}{t.command}{RESET}  {DIM}{t.purpose} ({t.phase}){RESET}{ver}")
+        if not t.present:
+            print(f"        {CYAN}{t.install_hint}{RESET}")
+    print()
+    return 0