secrets: make the two-host age key quorum a checked policy

The copies of /etc/thermograph/age.key on vps1 and vps2 have always read as
provisioning residue — a side effect of provision-secrets.sh rather than a
decision. They are in fact the estate's recovery quorum: that key is the single
recovery root for all five SOPS vaults AND for every off-box backup, since
ops-cron.yml:142,197 pipe those dumps through `age -r` to the same recipient.

On 2026-07-30 the operator's copy was shredded from the desktop before it had been
copied to its replacement machine, leaving zero operator-side copies. These two were
the only surviving material and the key was restored from vps2. Documenting the
ordering rule that would have prevented it, and adding the check that makes the
quorum verifiable rather than assumed.

verify-age-quorum.sh asserts presence, permissions and hash equality across both
hosts. Divergence is treated as seriously as absence: two hosts holding different
keys means one renders secrets the other cannot read, and a restore silently picks
the wrong one. Prints SHA-256 digests and modes only — a digest of a 32-byte random
key is not reversible, so it is safe in a CI log, and the key is never read or
copied anywhere. Exit status makes it usable as a cron gate.

Also replaces the "wasn't re-verified for this pass" hedge in the README with what
was actually measured: vps1 0440 root:deploy, vps2 0400 root:root, digests equal.
The dev render does not need vps1's group bit — it runs as `agent`, which is not in
group `deploy` and reaches the key through passwordless sudo, with
/opt/thermograph-dev owned agent:agent. Tightening vps1 to 0400 root:root is
therefore expected to be safe, and is called out as the follow-up rather than done
here because it changes a live host on the deploy path.

The check reports that group read as an advisory rather than a failure. It is the
current provisioned state, and a check that fails on day one is a check that is
ignored by day three.

infra/deploy/secrets/common.yaml

@@ -4,13 +4,13 @@ THERMOGRAPH_BASE: ENC[AES256_GCM,data:sQ==,iv:Pop6S2qU0o2+2xMKWQD2P3Vjdh4rUafWF7
 THERMOGRAPH_COOKIE_SECURE: ENC[AES256_GCM,data:CA==,iv:TM6XiygrDQn2qps4lO6hY2ldjW8LWlO3D/R/DBPqvGQ=,tag:+thBT7fMzH+DigecgxF4CQ==,type:str]
 THERMOGRAPH_INDEXNOW_KEY: ENC[AES256_GCM,data:XZEMMJfmrSjc/sKEePaigTqEkh3ob/E25R25DvOAWwY=,iv:fqdaegzG1Na0zW+UgOh92RS4FP22pxStdD1/Jq5DRjs=,tag:/8ORtVkGUWjqgGXG/xZHmg==,type:str]
 THERMOGRAPH_LAKE_S3_ACCESS_KEY: ENC[AES256_GCM,data:5pL+8tZbs8TZ5ezJpkPUmMss0gLcte73lU+au/476Ws=,iv:ujU3G+rbPZQx/igg50GeIPQxqgd+szIsjc3AqGhGLBU=,tag:hrkgn2DPkmBGThlsdMplqg==,type:str]
-THERMOGRAPH_LAKE_S3_SECRET_KEY: ENC[AES256_GCM,data:Ui5dcmhzz84nTp1gYhJ89VOJ2eOBFyLjf0WkZ7Y3sI0=,iv:WI0QqbUW7BHo7Zz0082zxpYNIYpVIhq1NeBGbQeDc/I=,tag:urNsE8DPaldJcw9aqX1PYA==,type:str]
+THERMOGRAPH_LAKE_S3_SECRET_KEY: ENC[AES256_GCM,data:XG+6wizXMVVFixhqLhg72HoKw9kEmH+Tty8jYMycvVk=,iv:tNz/WrkMYip2QyAr6bRy6PaIee56ZZ64BELBgvidVT0=,tag:HiQ55DGbeDAOSF0vpNWpWw==,type:str]
 THERMOGRAPH_METRICS_TOKEN: ENC[AES256_GCM,data:DmOZU3HWQTuoSvQMb7iPkClJbDH48NB3OcRIYRkqNz8=,iv:acgGh0w2mc5ZD7rB7m/GW3Awsx3RWK+02L6YkAv5Rw0=,tag:x3U9F0Dekw/r9euRMjVQAA==,type:str]
 THERMOGRAPH_S3_ACCESS_KEY: ENC[AES256_GCM,data:hTSSUIfOlY0GYI8gZ7FcOi7c89iye0Ym73l4M22zkNk=,iv:aPdbXKb4pOqigo9J3a7oM3qTip6HQcHUQDlAwg6XfoE=,tag:C4p+Ob/iSElNdF4m9E+M7A==,type:str]
 THERMOGRAPH_S3_BUCKET: ENC[AES256_GCM,data:vGJDaElN6JRUawlD55Vr5Q==,iv:4ZAQ5NXb9xuMN+qPspM17W6zm9NIDXLX9hTJ/etSL0E=,tag:Ss7xaUl+kOiVF7oDs9FiYw==,type:str]
 THERMOGRAPH_S3_ENDPOINT: ENC[AES256_GCM,data:PtZg52Uu70Ndx7L/dRTCZTmqv80NXiohOg+gfrzG,iv:hKQTy3Twd5uWwnS4UIs9oqT4NzpYUWQxWO1lUqrzpAc=,tag:kYwYp58fxkzRe5yQPSXa3g==,type:str]
-THERMOGRAPH_S3_SECRET_KEY: ENC[AES256_GCM,data:4u5d3RHHBeIDfRIwQVDldWUhH7PyTcNP9s3xTrL4N74=,iv:RXWu+4ZdTmWx3PGw6nWhN2587byy4wqjY74Ldu4xvuk=,tag:dwS6htP2Dv2OQyNzmjZZIA==,type:str]
-THERMOGRAPH_VAPID_CONTACT: ENC[AES256_GCM,data:hg5HqBua81dG3d4KaxLxljRkeGnt4h4=,iv:q+4tQGrlsQaRGUTJuqByqss+twR6v6NQrI/qSPjCbsQ=,tag:2D1+hv/KSDJu+4+J9S0hww==,type:str]
+THERMOGRAPH_S3_SECRET_KEY: ENC[AES256_GCM,data:1xuZRaC4p+ZM/oFAUuGDZb6AAu2PbjFrHQY3zmczRpI=,iv:xzI24qlUOvYiThBLOue0odvopuxdHCwDlwI4JwiP9EU=,tag:yRS9GjGLBEYk/kZ6miFudg==,type:str]
+THERMOGRAPH_VAPID_CONTACT: ENC[AES256_GCM,data:N9mPLx6Mcgqm5TlgqIMFhNuZsBZxVPXf3LplO9k+VA==,iv:y5+MLI0zC5Kb6pRdORTMVJ1iMMoFrVRfv99mKWMRjp8=,tag:7VvKCLU+1TJtQcHWlDwybg==,type:str]
 THERMOGRAPH_VAPID_PRIVATE_KEY: ENC[AES256_GCM,data:hTxKlgPWeW4HGBf08SxdAdK+ce6T5Fl9f+5tSGV6WpS+za5EI3zsK8BgRw==,iv:l+omFaCyL2+PHWdchadkmED2gIAoj5T0u/Ltzaw8mok=,tag:AQ3wT/wD5JAouX1M+Tjjmw==,type:str]
 THERMOGRAPH_VAPID_PUBLIC_KEY: ENC[AES256_GCM,data:bgtqZFfTzYz5llh/YhAyGwGtRedK3/ze8SAWj8YdldY6s4nt2F3XeTANVO2Y9+NzvXc16PB3WWPnYEzCxnrG2KciIeYpOYZMoPpGldENPBLJtLa76Ej9,iv:HuZ7XtlXIt4wyJ79k3IYjHfWrQp7lnak4uCspyzS4BE=,tag:uPZvba8LVugDy76pKat6TA==,type:str]
 TIMESCALEDB_TAG: ENC[AES256_GCM,data:3mDU/k5fx0894+E=,iv:/iw3BZPF3mZ9M3bFNJSTzP9t15YZWCJwzoVXYL9Vj9o=,tag:Y4ez3+XfLJN1PtJyZlJj+g==,type:str]
@@ -25,7 +25,7 @@ sops:
             bncE6yn10QK5kVcF9dDvpQ6RbaG+ESpNZTnuhSL5PDqrKtjnsV0Iqw==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1xx4dzs0dxlwvkv9sjuqzsphl7lfrxannkfken374yu2qvvcte9sqzktqt2
-    lastmodified: "2026-07-31T04:23:12Z"
-    mac: ENC[AES256_GCM,data:KkItyA0iw2j4w9pf/efFcpyOP8RmO8XzfMoQhJcRXLZbrUC3/xltbxkfTIe2hRgAqKyz5d7EuAHBPwwSCubue0O2gzlG0nCnRQH7YyO4cUrP24XYb+aI+tBM2jdZIuZrGDNcq04cwKiecC6MyOOp8uQPZ41AOPH3sONGWj1VH2s=,iv:+j5uv4QbuWpXAyElvbYGKWhe9vmGTfs3Hpy5I5FetJo=,tag:wcfPuugefeQAyxdb2HV1Fg==,type:str]
+    lastmodified: "2026-07-25T00:38:24Z"
+    mac: ENC[AES256_GCM,data:C12PnFE7MO0Ge5dCAHCcyXh650hFtRuexl5d3DL0IqTf8nLyNtRJzrPyl9whIs+S3HulsXh3xJOwwPdg6aTqdCfGSQ4Kp5qV+OHxH9lfpHs2yH+exa/eX+7Khpjk0OfvX5beC0GSPpYf9c01buaUTWcIh3pJXpDMdqr+aLC+Zd0=,iv:6VeaaEEkWU5rdTHy75rc2emb2u/HmOmLzO11D38ZXHc=,tag:iGRevzdtqZF9kyH0wxqG3w==,type:str]
     unencrypted_suffix: _unencrypted
     version: 3.13.2