Bump tangled to latest master (post-v1.13.0-alpha) and pin in auto-update

The tangled core was on rev 956f97c (v1.11.0-alpha) and v1.13.0-alpha
introduces automatic DID minting for repositories which we want.

Master HEAD (6a27cd2) is post-v1.13.0-alpha and includes the DID
auto-mint migration. After deploy, retry verification on the knot
dashboard at https://tangled.org/settings/knots.

Note: the build's reported version string is hardcoded to 1.11.0-alpha
in nix/pkgs/knot-unwrapped.nix upstream -- this is a stale label, but
the actual code includes v1.13.0-alpha features (DID minting schema in
knotserver/db/db.go).

Also add an explicit `nix flake update tangled` to auto-update.nix so
tangled is always tracked, independent of how other inputs are pinned.

flake.lock

@@ -188,11 +188,11 @@
         "lastModified": 1731402384,
         "narHash": "sha256-OwUmrPfEehLDz0fl2ChYLK8FQM2p0G1+EMrGsYEq+6g=",
         "type": "tarball",
-        "url": "https://github.com/IBM/plex/releases/download/@ibm/plex-mono@1.1.0/ibm-plex-mono.zip"
+        "url": "https://github.com/IBM/plex/releases/download/@ibm%2Fplex-mono@1.1.0/ibm-plex-mono.zip"
       },
       "original": {
         "type": "tarball",
-        "url": "https://github.com/IBM/plex/releases/download/@ibm/plex-mono@1.1.0/ibm-plex-mono.zip"
+        "url": "https://github.com/IBM/plex/releases/download/@ibm%2Fplex-mono@1.1.0/ibm-plex-mono.zip"
       }
     },
     "indigo": {
@@ -351,11 +351,11 @@
         "sqlite-lib-src": "sqlite-lib-src"
       },
       "locked": {
-        "lastModified": 1776427995,
-        "narHash": "sha256-bUR/cHqZP1zigWCo59KFF+F6UDuGM9q5CiFHdvnvSO8=",
+        "lastModified": 1777129244,
+        "narHash": "sha256-4+f+RrVXbtBRuffJg6QyANOc/H9MMpp9PjnxwlUU6Hk=",
         "ref": "refs/heads/master",
-        "rev": "956f97c314517efbfa18d04ce8e0234e6609a30a",
-        "revCount": 2250,
+        "rev": "6a27cd259b67bdad85e8d82a31543cc11c309fc6",
+        "revCount": 2274,
         "type": "git",
         "url": "https://tangled.org/@tangled.org/core"
       },