chore(secrets): Phase 4 — remove stale sops.yaml anchors and re-encrypt

Remove four stale age key anchors from .sops.yaml that correspond to
non-lxc build-type variants that were never deployed (or are now
superseded by their lxc-* counterparts):

  &docker   → superseded by &lxc-docker (active running host)
  &server   → superseded by &lxc-server (active running host)
  &nix-cache → superseded by &lxc-nix-cache (active running host)
  &nix-minimal → superseded by &lxc-minimal (active running host)

Also remove the secrets/docker.yaml creation_rules block entirely since
that file does not exist.

Re-encrypt secrets/common.yaml, secrets/nix-cache.yaml, and
secrets/server.yaml with sops updatekeys to drop the stale recipients.
The four removed keys can no longer decrypt these files.

Update README.md and CLAUDE.md to clarify that deployed lxc-* hosts
now use clan vars (vars/per-machine/<target>/openssh/) rather than the
gitignored host-keys/ directory.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B2EJ4qTsM5KUqhS5c3GAwx

secrets/nix-cache.yaml

@@ -4,47 +4,38 @@ sops:
     age:
         - enc: |
             -----BEGIN AGE ENCRYPTED FILE-----
-            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBMWjdNblFJdUpyMGFrSWJm
-            a21ESTZTK05YNk5CWFlKNlhIdXhIUFhQNVR3CnZZK1N2N3VKVWs5ZGxZaUhCb1VP
-            dlJaNXM2alNiUG42NlFqeVV3WDdtbnMKLS0tIFpvTlBZU2RpNUtoNVoxeUdKU2Zt
-            QjFydW1xeDd6N2xBU2lhRmtuREhkNDQK49/mcHVCj9tBtGe1ZnK14YWHCtgzBBvV
-            giDA8BzThifXjWtL8zF60kibKFVRGrsRZT38tRuv5QKzu6Z5Cbc+2g==
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBwMklZTFJuR3NYbkFvV0l0
+            eUhMWU4vMHpnN1NKVThuVVdiOFpkZW9rTjBVCjJabWkvOFpOSm1hdEdlZTYxc3BP
+            WkRURDFEQzMvRFlka1VnaU9zRjhiSEkKLS0tIHZXRG9GaE5iVjg3M3I0SzhtN0JP
+            UlJVUzRzN3NEZWxXZHJ6RW1oYWwxS2MKonnhq7YDg4v93PZtoaLANDy8mdRCenjo
+            FjRUzozMLpgWBll4DwRWikejsrRofRBwlcsiIdrBr90f8Lr9pHdQ/Q==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1njap586hc0q43kr03g6c8eqhdsmk8zcafkl3f83xwlc2gqhlmfgs4tmwad
         - enc: |
             -----BEGIN AGE ENCRYPTED FILE-----
-            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBkZmtLL3pzbmNBNkkzRDhF
-            MFZrS3FlZ3I0ZlNJbVN4aUpxYkQ5VkRSYlRjCnUxM0tqRFJDMis0TDd6cUthN0ZE
-            eTBrSDd4a1BzNHZqZVJIc3V4NzBoeGsKLS0tIE9ENFBWUUtadC9vQ1UyRmFLWG9B
-            UUZLeThnUzBNRSttemtuaTN1NWlkUVkKbDeId9JVSvjszcA0TT4L9C4IB5xLCuJK
-            ESqfwJe7QoTBpYA3RMmtIcYK3oYX9KKGrdUU0J+TV0Flr6wqHBHbOQ==
-            -----END AGE ENCRYPTED FILE-----
-          recipient: age120le4a5l8dh3lyfgvmj3d9ksmej6ajs5mer5y7r0vfg3x9fn69dqf8xgzu
-        - enc: |
-            -----BEGIN AGE ENCRYPTED FILE-----
-            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSA4OVJvSTVkcDdMQW9HdXcz
-            bmVOVjQvYU81MExSZ3NtUzZTNHNRb1VjNmljCkZ6bDN1OGx4NkhGVENOTjQxWFVy
-            QWNNbENkMVpOTS90dzFWalVtczZ1YU0KLS0tIFZSQVNkUGE0TERyQ1BPTjVQUEdN
-            Y2tFOXlkRHhGTmNWVDZWRnQ5dTNTM1EKNEZZqO6mmj3GnJJ0/8UrisHODEKPjyah
-            aAi5rMnEDAniqyouTP1Mq3GOn67KoESqZX4qY3nHvJC7QBIDii3sBg==
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBsWDJQYzM5Z1JRT3FlVkJy
+            TkVaSXdzanYwbnpOM1d2RFh0c2NaSUFmdW1ZCit4SVFxSS9HNXhVM2gveERGVS81
+            NVFQaUV2RGR5Q3kyUTQ5eEpDVXJVMWcKLS0tIHdHSy9WM0o3Q0o1THhXZW11K2Vp
+            NTNtSGM2UDFuWDBEdS9tbTY1ZWt6UlUK8z5qoi0kGn0ES3m9khummuU51rkR0Sb9
+            TWT92+BWvPdNrAsDFjv0fgpUKyTMzN72EzHZKAJCIM3crUG9I0tX2g==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1jcx3yajjhghn8qh8za3yeu8nxykzlg3p4nrv03vnfvzl0mzayg2qmg940e
         - enc: |
             -----BEGIN AGE ENCRYPTED FILE-----
-            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSB5aW8rZG5MenF5RmFWdUgx
-            dk1oV3BpYmNGUnJHTkhOVjVVM0k1T2hlQkdjCm9xYXNkVWkrTWloWEtRcmRuUUkr
-            NUEyZ0ZFeFZ0M2dHUTNYdzFVQ2pDS2MKLS0tIGNnaXcxUUo0cGE4T28vdGJPT1d5
-            SnliakxSZjBNQlpjSlNJelVWVUJORDgKWVuK6VYN5BySdRLHLlU0Sk6PPAsz5lVS
-            Vw96AbKrmczhkiYUWGacde0KjBJb/7tyfXeckV1iqj1/6vT03dDNlA==
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBpY3o4SEpwZEdFQmVnOTVV
+            d2NqL0VudHM4VjdDK1N4dWdlS0lGR1V6a0c0CmJUTHlsbEMwaEU0Kzdaa21lRFRm
+            RTRnTUlGUG9GQVB4U2pzTHdRY09udkEKLS0tIGlFQW9Wd0N5WFg2WUpCQzhWUm5v
+            aG1VVWV5ajBmc2o4ckgyQWpWaFVxVmcKisAw40bGQBRH+u6uNygfYpfb7iEgfEHj
+            E+g9n2WeVH8kUzD2O1o6VAu4m/SVuI4+IQ77j9GEWmlI/wgp8wKXgQ==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1ufg390ydrmma849t9xfkxxl5xvdkk6mngnlzhmy7mvuaje8sgcmsmnq6l7
         - enc: |
             -----BEGIN AGE ENCRYPTED FILE-----
-            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBCckVtTWtCSWpxSGFEbWI5
-            MkVkeTRYN1MzMEk2L1RQemRvM1RSaEVpakVNCjBsbm5qcDFlRXRCQXNkQTd2Snlk
-            WW51Sm1xYjJldmJ0R09WR0hHbWk3NWMKLS0tIGlWYk4zNElVQk9qcGJUUUptMVZV
-            aStXT2lVNXlwRG54SmhxV21tb2M3NzAK2nlgUrlarGERUClDvytMXwPO5e+zaIlW
-            T68ePI4e1vh2qj5xpjXoK5Pzv6oUcjhB0P7Ij2lA8bRdFLWfHPAqvA==
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSB1elpNZXVJbmJWSU85aUV6
+            NG9YTWVBeWxiRHUveStTQnl4NC8rT2VNdHpNCldxZVJYNVhUR2V3Vk41VnJxenVT
+            WS9rRWlKcGpVdVJPakkwUTY2a2xQTlkKLS0tIFhFVTRucFNuS0pMK0FNRk1ndnFO
+            SlVvakczaktUa2VLY3RLYUdVRzFyamcKIhctg0mbYL7OE08dRwj5wMu2x+O8/BMu
+            IqA477+noQ/Rjrszb2hEvxID7keogcDUWMWQzQvdMc22+3mvAr9qIg==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1jlltcv5jcnm40z5k0q6hv053k2rqpqvemtuecdwn527uw8uqz4es3x7m68
     lastmodified: "2026-07-19T23:30:21Z"