Add Gitea SSH setup script and integrate Gitea into partnership/failover

Partnership/gitea_ssh_setup.sh: generates ed25519 keypair, registers public key
  with Gitea API (POST /api/v1/user/keys), tests SSH connection, writes ~/.ssh/config
  entry. Idempotent — skips steps already done. --force regenerates and re-registers.
  Resolves Gitea endpoint from container IP first, falls back to GITEA_DOMAIN.

common.sh: alias HOST*_GITEA_API_TOKEN → GITEA_API_TOKEN in detect_hosts().
  Add to detect_hosts() doc comment.

master.conf: add GITEA_HTTP_PORT=3000 for API endpoint construction.

host1.conf: add HOST1_GITEA_API_TOKEN (fill in from Gitea Settings → Applications).
  Add my-Gitea.xml to HOST1_PARTNERSHIP_AUTH_STACK — onboard pushes it to HOST2.

host2.conf: add Gitea to FALLBACK_HOST2_COVERS_HOST1_TIER1 — starts immediately
  when HOST1 goes down, making the source of truth reachable independently of
  HOST1's auth stack.

master.conf

@@ -249,6 +249,7 @@
     TARGET_DIR="/mnt/user/appdata/unraid_scripts"
     GITEA_SSH_KEY="/root/.ssh/unraid_gitea"
     SSH_PORT=221                            # Gitea SSH port (default 22, Gitea often uses 221/222)
+    GITEA_HTTP_PORT=3000                    # Gitea web/API port — used by gitea_ssh_setup.sh
 
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