feat: multi-distro support and tagged golden snapshots

Add Alpine, Debian, and Ubuntu rootfs support to `init [distro]`.
Golden snapshots are now namespaced under `golden/<tag>/` so multiple
baselines can coexist. `spawn [tag] [N]` selects which snapshot to
clone from. Systemd-based distros (Debian, Ubuntu) get a fc-net-init
systemd unit; Alpine keeps its inittab-based init.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

orchestrator/web/terminal.html

@@ -79,6 +79,28 @@
     #spawn-btn:hover:not(:disabled) { background: #243e24; }
     #spawn-btn:disabled { opacity: .5; cursor: default; }
 
+    #spawn-controls {
+      display: flex;
+      gap: 0.5rem;
+      align-items: center;
+    }
+
+    #tag-select {
+      background: #1a1a1a;
+      border: 1px solid #444;
+      border-radius: 4px;
+      color: #8be;
+      padding: 0.4rem 0.8rem;
+      font-family: monospace;
+      font-size: 0.9rem;
+      outline: none;
+      transition: border-color .15s, background .15s;
+      cursor: pointer;
+    }
+    #tag-select:hover { background: #222; }
+    #tag-select:focus { border-color: #8be; }
+    #tag-select:disabled { opacity: .5; cursor: default; }
+
     #error-msg {
       color: #c44;
       font-size: .85rem;
@@ -119,7 +141,10 @@
   <h1>fc-orch console</h1>
   <ul id="clone-list"></ul>
   <p class="none" id="no-clones" style="display:none">No running clones.</p>
-  <button id="spawn-btn">+ Spawn clone</button>
+  <div id="spawn-controls">
+    <select id="tag-select"></select>
+    <button id="spawn-btn">+ Spawn clone</button>
+  </div>
   <p id="error-msg"></p>
 </div>
 
@@ -143,6 +168,7 @@
     const ul      = document.getElementById('clone-list');
     const noneEl  = document.getElementById('no-clones');
     const spawnBtn = document.getElementById('spawn-btn');
+    const tagSelect = document.getElementById('tag-select');
     const errEl   = document.getElementById('error-msg');
 
     function showError(msg) {
@@ -203,7 +229,7 @@
       fetch('/clones', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify({ net: true }),
+        body: JSON.stringify({ net: true, tag: tagSelect.value }),
       })
         .then(r => {
           if (!r.ok) return r.text().then(t => { throw new Error(t); });
@@ -219,7 +245,37 @@
         });
     });
 
+    function refreshTags() {
+      fetch('/tags')
+        .then(r => r.json())
+        .then(tags => {
+          tagSelect.innerHTML = '';
+          if (!tags || tags.length === 0) {
+            const opt = document.createElement('option');
+            opt.value = '';
+            opt.textContent = 'No golden VMs';
+            tagSelect.appendChild(opt);
+            tagSelect.disabled = true;
+            spawnBtn.disabled = true;
+            return;
+          }
+          tagSelect.disabled = false;
+          spawnBtn.disabled = false;
+          tags.forEach(t => {
+            const opt = document.createElement('option');
+            opt.value = t;
+            opt.textContent = t;
+            if (t === 'default' || t === 'alpine') opt.selected = true;
+            tagSelect.appendChild(opt);
+          });
+        })
+        .catch(e => {
+          console.error("fetch tags failed:", e);
+        });
+    }
+
     refreshList();
+    refreshTags();
     return;
   }