headscale: add OIDC login, stop overriding clients' local DNS

Two changes to the control server, plus the fallout on the hosts.

OIDC via Authentik, so `tailscale up --login-server ...` opens a browser
instead of needing a pre-auth key. This is a second Authentik application,
separate from headplane's, with headscale's own /oidc/callback redirect.
Headless hosts keep using pre-auth keys. Note that headscale runs OIDC
discovery at startup and a failure is FATAL -- pointing `issuer` at an
application that does not exist yet means the control server will not
boot, so verify the discovery document before deploying.

override_local_dns = false, because the upstream default of true replaces
resolv.conf with 100.100.100.100 on every node. That silently broke the
LAN's `.sol` names -- pihole serves those and the global nameservers
return NXDOMAIN for them -- and took ad blocking down with them. It also
made each node's entire DNS depend on tailscaled, which is what had
forced --accept-dns=false onto neptun and mercury individually; both of
those workarounds are now removed, and with MagicDNS resolving properly
again neptun no longer needs its hardcoded /etc/hosts pin for jupiter.

Also serves jellyfin and seerr from jupiter, matching the ports they
already use on its LAN vhosts, and rotates the tailnet pre-auth keys.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

secrets/jupiter.yaml

@@ -1,6 +1,6 @@
 samba_password: ENC[AES256_GCM,data:K3FtKC0CrOLMyfQokmxxlyUnDPo=,iv:9bTE/S/i05LJYldOHuBuz3+g8JdTuq0ysFFgXOmfti8=,tag:77NIxy7qpHRqCmbOR83AfA==,type:str]
 darman_password: ENC[AES256_GCM,data:DOHHlM4Qdw4WgkN+/M51n2LMjJqq5MS0FeGEH8Pz3297yUZ8jBDOKRS/Tek9stC05JKEQRtn/vVVbAY0nXs20MwrsDMo+IEFXx7Ms90vVyYIYe5O5/0aQkPq84vcwGN0RW1Rj5Y3s38vWA==,iv:DAqHbvOBq7FT7ALbmBXJ0HadEGEsL8V2e7R99H5ZH0s=,tag:9XpiRFIbaZjMn59uHCOA1g==,type:str]
-tailscale_authkey: ENC[AES256_GCM,data:LjRXyFW1SbhUiXbCQnRKinJluGfQWsjS7TTP/TMvx2noP6aFNrcYMvitG+OqLAlNEQAy0bcxZejZgJN+yNS+5iuy2F7OXhrpO7Df0JHkyMvQpnaH2XBEsw==,iv:QxVkB6GtZOYWFAOFVdBQMU2Hb/2OwBRCLHdfxoDF/ME=,tag:PBL0TV6yZJSu4+TGpycf/A==,type:str]
+tailscale_authkey: ENC[AES256_GCM,data:dwBoHIJNcRSLxk1rbMsrEHVoYdxdnvYpPq44utfQ8t4XkXEzto96FEctv/QuPYVGgUxdyPczmc0/97m4AAKjaBVGFXpt/XlnFQI2XgzgSJ0qhNWyfJ1F/g==,iv:1b9nMeeZwr4O8cKjxQ0f+j/yxMUBZpicmdXw7bb9hZk=,tag:FWgrKtKgqailQk+BcZNXhw==,type:str]
 mediamanager_token_secret: ENC[AES256_GCM,data:g75vj1E6B029O076yV3DS/1z99Tq6wMhEVx+ULYDjHsplyA+vqVRvBlviC64V47IMqKd9k2eTGBJ98Ptv3UIjbr446xZinz0c7PZgHU0XOX4EUcB1ORloMFZIv1zUv8VRjUISUQnn/vRk60e7u8eXrOrgXjxfnoBKrdKZmqxhAM=,iv:2t0XBExC9RvbTomezka+99/LtJl64zNwneA7WWc4ju0=,tag:SVCYuw0n6JevnvoQOIkjPw==,type:str]
 sabnzbd_api_key: ENC[AES256_GCM,data:6UW1u2Ikmnq34t4H4k/4C44SJeFHRlaPjWwUjEfH1GQ=,iv:sGsd8Sd2pfUhTUDg6PlRzfVYejRbF69jmDTIa2fvY4M=,tag:3fOLgU1K1gKHxQ3J1+3oRQ==,type:str]
 prowlarr_api_key: ENC[AES256_GCM,data:ab1QACaagI8ACJXFUy8r9X9lgYwRo1byUmhBPSRWwKk=,iv:EcuF6EN/4mWxlXi6R1qDzv4rOw6AT+OGSNQaaBwjJHg=,tag:hixHrbQWU6QQZNMM5rNDsg==,type:str]
@@ -25,7 +25,7 @@ sops:
             CzjSDQZTcseEXZNwuzZcfB5Mvq0BQvjOj7lGuxzuE4qwWkdJWGfVLQ==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1zak7glavmg4026p2389fyqe769vqm4jrryknuqckgqq4merz5f7q44rkkt
-    lastmodified: "2026-07-20T07:51:55Z"
-    mac: ENC[AES256_GCM,data:CBQrHpdIOn35CIrZaqZqZd/V4pp+bMNygXJoYwlOvwAtb49ElqmQgSZxWVgTKpTNZpMkqYie6HQB0c4vsmU/BYeLQKJNYBQvBxIrTQr4wMURj2jBMhtVT2osX5cUpNakoHZUdz6ARXyYGEVOBzMY77vSxk6VkVi5CFmeOETkcik=,iv:a6iTeIlR2S65pTrH+juS6kEhpbiaAmhcPLssasUPZ58=,tag:QP+LMclWU9SO5/uPI/Nwwg==,type:str]
+    lastmodified: "2026-07-20T18:42:14Z"
+    mac: ENC[AES256_GCM,data:l9O/KAd/5KfC+LXwE2y5+ybflyy9Xl0PikoRfcOzIFu+fVWESyi0D22emWen6J4mpvsXgjAp4GCu4RKNTGyy47mfkaHh/KdxozEOmP8VlKOJXtqzU9lTgZwhHqkF9RKsRLKHvmREugwzWnpplJ8J7bg5Z3llBIM36FlElzQ9hUw=,iv:x0lM9Ctcn1XCsXftB9Ze8WV8Rp4YA26MQ/AdGC78MyY=,tag:gtfaSDQAcAkngRw2Ph2N0A==,type:str]
     unencrypted_suffix: _unencrypted
     version: 3.13.1