release(v1.7.31-alpha): idempotent IndeedHub install + auto-merge default mirrors/registries + 3rd OVH update mirror

- Backend: install.rs registry reachability probe now strips the
  `host[:port]/namespace` suffix before appending `/v2/` (the Docker
  V2 API lives at the host root, not under the namespace) and accepts
  HTTP 405 in addition to 200/401 as "registry daemon alive". This
  fixes false "unreachable" reports on the Test button for Gitea and
  other registries that protect their /v2/ endpoint.
- Backend: stacks.rs install_indeedhub_stack now force-removes any
  leftover indeedhub-* containers and indeedhub-net before creating
  the stack. A partial install (or the old first-boot stub racing the
  installer) used to leave containers around that blocked re-install
  with "name already in use". Re-running the App Store install now
  self-heals.
- Backend: registry.rs load_registries auto-merges any default
  registry URLs missing from the saved config (appended with priority
  max+10+i, persisted). Lets new default mirrors (e.g. Server 3 OVH)
  roll out to existing nodes without manual config edits. Explicit
  removals still stick — URLs absent from disk AND absent from
  defaults stay gone.
- Backend: update.rs adds DEFAULT_TERTIARY_MIRROR_URL at
  http://146.59.87.168:3000/ (Server 3 OVH) to default_mirrors, with
  the same auto-merge-on-load behavior as registries. Test updated
  for 3-mirror default (.160, tx1138, .168).
- Scripts: dropped the first-boot IndeedHub stub (~38 lines in
  first-boot-containers.sh §8b). It predated the proper stack
  installer, raced it, and was the main source of the name-conflict
  mess the stacks.rs cleanup above now also guards against.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/Cargo.lock

@@ -80,7 +80,7 @@ checksum = "a23eb6b1614318a8071c9b2521f36b424b2c83db5eb3a0fead4a6c0809af6e61"
 
 [[package]]
 name = "archipelago"
-version = "1.7.30-alpha"
+version = "1.7.31-alpha"
 dependencies = [
  "anyhow",
  "archipelago-container",