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/archipelago/src/update.rs

@@ -68,6 +68,10 @@ const DEFAULT_UPDATE_MANIFEST_URL: &str =
 /// is slow or unreachable.
 const DEFAULT_SECONDARY_MIRROR_URL: &str =
     "http://23.182.128.160:3000/lfg2025/archy/raw/branch/main/releases/manifest.json";
+/// Tertiary mirror on a separate OVH VPS — independent network path so
+/// a single-provider outage doesn't knock out all three mirrors.
+const DEFAULT_TERTIARY_MIRROR_URL: &str =
+    "http://146.59.87.168:3000/lfg2025/archy/raw/branch/main/releases/manifest.json";
 const UPDATE_STATE_FILE: &str = "update_state.json";
 const UPDATE_MIRRORS_FILE: &str = "update-mirrors.json";
 
@@ -97,13 +101,24 @@ fn default_mirrors() -> Vec<UpdateMirror> {
             url: DEFAULT_UPDATE_MANIFEST_URL.to_string(),
             label: "Server 2 (tx1138)".to_string(),
         },
+        UpdateMirror {
+            url: DEFAULT_TERTIARY_MIRROR_URL.to_string(),
+            label: "Server 3 (OVH)".to_string(),
+        },
     ]
 }
 
 /// Load the operator-configured mirror list. Returns defaults if the
 /// file doesn't exist yet, so a node OTA'd from a pre-mirrors release
-/// starts with both Server 1 and Server 2 available without any manual
-/// config.
+/// starts with the current default mirrors available without any
+/// manual config.
+///
+/// Migration: any default mirror URL that isn't already in the saved
+/// list gets appended at the end. This lets us add new default mirrors
+/// (e.g. a new Server 3) and have them appear on existing nodes after
+/// an update, without requiring manual config edits. Explicit removals
+/// stick — once an operator removes a URL it stays gone unless it's
+/// later re-added to defaults.
 pub async fn load_mirrors(data_dir: &Path) -> Result<Vec<UpdateMirror>> {
     let path = mirrors_path(data_dir);
     if !path.exists() {
@@ -112,13 +127,27 @@ pub async fn load_mirrors(data_dir: &Path) -> Result<Vec<UpdateMirror>> {
     let bytes = fs::read(&path)
         .await
         .with_context(|| format!("read {}", path.display()))?;
-    let list: Vec<UpdateMirror> =
+    let mut list: Vec<UpdateMirror> =
         serde_json::from_slice(&bytes).with_context(|| format!("parse {}", path.display()))?;
     if list.is_empty() {
-        Ok(default_mirrors())
-    } else {
-        Ok(list)
+        return Ok(default_mirrors());
     }
+
+    // Merge in any default URLs the saved config is missing.
+    let known: std::collections::HashSet<String> =
+        list.iter().map(|m| m.url.clone()).collect();
+    let defaults = default_mirrors();
+    let mut added = false;
+    for def in &defaults {
+        if !known.contains(&def.url) {
+            list.push(def.clone());
+            added = true;
+        }
+    }
+    if added {
+        let _ = save_mirrors(data_dir, &list).await;
+    }
+    Ok(list)
 }
 
 pub async fn save_mirrors(data_dir: &Path, mirrors: &[UpdateMirror]) -> Result<()> {
@@ -1187,9 +1216,10 @@ mod tests {
     async fn test_load_mirrors_returns_defaults_when_absent() {
         let dir = tempfile::tempdir().unwrap();
         let list = load_mirrors(dir.path()).await.unwrap();
-        assert_eq!(list.len(), 2);
-        assert!(list[0].url.contains("git.tx1138.com"));
-        assert!(list[1].url.contains("23.182.128.160"));
+        assert_eq!(list.len(), 3);
+        assert!(list[0].url.contains("23.182.128.160"));
+        assert!(list[1].url.contains("git.tx1138.com"));
+        assert!(list[2].url.contains("146.59.87.168"));
     }
 
     #[tokio::test]