refactor: Restructure ~/.castle/ as the instance directory

Move all instance state into ~/.castle/ with clear separation:
- code/        — user project source (was components/)
- artifacts/   — generated specs, built content (was generated/, static/)
- data/        — service runtime data (was /data/castle/)
- secrets/     — credentials

castle.yaml moves to ~/.castle/castle.yaml as the canonical location.
Source paths use repo: prefix for git repo programs (castle-api, app)
and relative paths for user projects (code/central-context).

Add idempotent install.sh for bootstrapping infrastructure (Docker,
Caddy, MQTT, Postgres, Neo4j) with interactive service detection.

Remove components/ from repo (now in ~/.castle/code/), deinit
submodules, remove .gitmodules.

castle-api/src/castle_api/config_editor.py

@@ -274,11 +274,11 @@ async def apply_config() -> ApplyResponse:
             errors.append(f"Failed to restart {name}: {output}")
 
     # Reload gateway
-    from castle_core.config import GENERATED_DIR, ensure_dirs
+    from castle_core.config import SPECS_DIR, ensure_dirs
     from castle_core.generators.caddyfile import generate_caddyfile_from_registry
 
     ensure_dirs()
-    caddyfile_path = GENERATED_DIR / "Caddyfile"
+    caddyfile_path = SPECS_DIR / "Caddyfile"
     caddyfile_path.write_text(generate_caddyfile_from_registry(registry))
     actions.append("Generated Caddyfile")
 

castle-api/src/castle_api/routes.py

@@ -8,7 +8,7 @@ from pathlib import Path
 
 from fastapi import APIRouter, HTTPException, status
 
-from castle_core.config import GENERATED_DIR
+from castle_core.config import SPECS_DIR
 from castle_core.generators.caddyfile import generate_caddyfile_from_registry
 from castle_core.manifest import ProgramSpec, JobSpec, ServiceSpec
 from castle_core.stacks import available_actions
@@ -834,8 +834,8 @@ def get_caddyfile() -> dict[str, str]:
 async def reload_gateway() -> dict[str, str]:
     """Regenerate Caddyfile and reload Caddy."""
     registry = get_registry()
-    GENERATED_DIR.mkdir(parents=True, exist_ok=True)
-    caddyfile_path = GENERATED_DIR / "Caddyfile"
+    SPECS_DIR.mkdir(parents=True, exist_ok=True)
+    caddyfile_path = SPECS_DIR / "Caddyfile"
 
     # Include remote registries for cross-node routing
     remote_regs = {h: n.registry for h, n in mesh_state.all_nodes().items()}