Retire gateway.tls=internal; host routes use a bare subdomain label

acme mode fully replaced the internal-CA path (which required installing a private
CA on every device — the exact pain, esp. on Android, that acme avoids). Remove
`internal` entirely and simplify how services declare host routes.

- Generator (caddyfile.py): drop the `tls internal` branch — modes are now
  `off` | `acme`. In acme mode the published subdomain is the **first DNS label**
  of `proxy.caddy.host` (a bare `claw`, or a legacy `claw.civil.lan`, both →
  `claw.<domain>`), so services stay domain-agnostic and the declared value is
  authoritative again (no more silent service-name override). Shared
  `_host_matcher_block` reused by off-mode and the acme wildcard site.
- castle-api: delete `GET /gateway/ca.crt`, `_gateway_ca_pem`, `_ca_fingerprint`
  and the now-unused imports; drop `ca_fingerprint` from `GatewayInfo` (keep
  `tls`).
- Dashboard: remove the CA-cert download button + unused imports; drop
  `ca_fingerprint` from the `GatewayInfo` type.
- Tests: replace TestCaddyfileTlsInternal with an off-mode class (keeps the
  runner-agnostic host-route coverage); acme tests assert first-label derivation
  incl. label-wins-over-service-name; drop the castle-api CA-endpoint test.
- Docs: registry.md + dns-and-tls.md — two-mode tables (off|acme), remove the
  internal sections/CA-download, document the bare-label host convention; note a
  domain-less node stays on `off`.

castle-api/src/castle_api/routes.py

@@ -3,15 +3,10 @@
 from __future__ import annotations
 
 import asyncio
-import hashlib
-import json
-import os
 import shutil
-import ssl
-import urllib.request
 from pathlib import Path
 
-from fastapi import APIRouter, HTTPException, Response, status
+from fastapi import APIRouter, HTTPException, status
 
 from castle_core.config import SPECS_DIR
 from castle_core.generators.caddyfile import generate_caddyfile_from_registry
@@ -899,13 +894,6 @@ def get_gateway() -> GatewayInfo:
     # Caddyfile order is precedence-sensitive; the displayed table is alphabetical.
     routes.sort(key=lambda r: r.address)
 
-    tls = registry.node.gateway_tls
-    ca_fingerprint = None
-    if (tls or "").lower() == "internal":
-        pem = _gateway_ca_pem(registry.node.gateway_tls)
-        if pem:
-            ca_fingerprint = _ca_fingerprint(pem)
-
     return GatewayInfo(
         port=registry.node.gateway_port,
         hostname=registry.node.hostname,
@@ -913,8 +901,7 @@ def get_gateway() -> GatewayInfo:
         service_count=service_count,
         managed_count=managed_count,
         routes=routes,
-        tls=tls,
-        ca_fingerprint=ca_fingerprint,
+        tls=registry.node.gateway_tls,
     )
 
 
@@ -925,66 +912,6 @@ def get_caddyfile() -> dict[str, str]:
     return {"content": generate_caddyfile_from_registry(registry)}
 
 
-# Caddy's admin API exposes the local CA's root cert — the authoritative source,
-# matching the running gateway (same endpoint `caddy trust` uses).
-_CADDY_ADMIN = "http://localhost:2019"
-
-
-def _gateway_ca_pem(gateway_tls: str | None) -> str | None:
-    """The gateway's local-CA root certificate (PEM), or None.
-
-    Only the public root cert — never the CA private key. Returns None unless
-    `gateway.tls` is "internal" and a CA exists. Prefers Caddy's admin API (the
-    running gateway's actual CA); falls back to the on-disk root.crt.
-    """
-    if (gateway_tls or "").lower() != "internal":
-        return None
-    try:
-        with urllib.request.urlopen(f"{_CADDY_ADMIN}/pki/ca/local", timeout=2) as resp:
-            data = json.loads(resp.read())
-        pem = data.get("root_certificate")
-        if pem:
-            return pem
-    except Exception:
-        pass  # admin API down → try the file
-    base = os.environ.get("XDG_DATA_HOME") or str(Path.home() / ".local" / "share")
-    root = Path(base) / "caddy" / "pki" / "authorities" / "local" / "root.crt"
-    if root.is_file():
-        return root.read_text()
-    return None
-
-
-def _ca_fingerprint(pem: str) -> str | None:
-    """Colon-separated uppercase SHA-256 of the cert DER, for out-of-band verify."""
-    try:
-        der = ssl.PEM_cert_to_DER_cert(pem)
-    except Exception:
-        return None
-    hexd = hashlib.sha256(der).hexdigest().upper()
-    return ":".join(hexd[i : i + 2] for i in range(0, len(hexd), 2))
-
-
-@router.get("/gateway/ca.crt")
-def get_gateway_ca() -> Response:
-    """Download the gateway's local-CA root cert so clients can trust *.lan HTTPS.
-
-    Public certificate only (the CA private key never leaves the host). 404 when
-    the gateway isn't serving internal-CA TLS or no cert has been issued yet.
-    """
-    registry = get_registry()
-    pem = _gateway_ca_pem(registry.node.gateway_tls)
-    if not pem:
-        raise HTTPException(
-            status_code=404,
-            detail="No gateway CA (gateway.tls is not 'internal', or no cert yet).",
-        )
-    return Response(
-        content=pem,
-        media_type="application/x-x509-ca-cert",
-        headers={"Content-Disposition": 'attachment; filename="castle-root.crt"'},
-    )
-
-
 @router.post("/gateway/reload")
 async def reload_gateway() -> dict[str, str]:
     """Regenerate Caddyfile and reload Caddy."""