feat(inference): S7 Call 1/Call 2 + prompt revision REST + test-inference + Generate text UI

- backend/inference.py: prompt seed (rev 0) + append-only revision REST
  (POST /prompts/{call}/revisions, /activate, GET; METADATA-105/106). Call 1 vision
  classification (1024px processed photos + synced taxonomy, 0.7 confidence gate,
  METADATA-35/40/45), Call 2 long description (user-triggered, METADATA-55/60/65),
  inference_log per call (METADATA-66), inference-off server_description (METADATA-70),
  test-inference probe (SETTINGS-45). Stdlib urllib, no new deps.
- frontend: create/inference/GenerateText.svelte (control visible only when content
  enabled + endpoint reachable, METADATA-110; Call 2 + Call 1 buttons) + dev toggle.
- tests: 6 inference tests (seed+revision, call1 gate, call2 stores desc, off->409,
  server desc, test-inference unconfigured).

Verified: pytest 54 passed; gates exit 0; npm build ok.

frontend/src/create/inference/GenerateText.svelte

@@ -0,0 +1,103 @@
+<script lang="ts">
+  let slabId = '';
+  let contentEnabled = false;
+  let reachable = false;
+  let description: string | null = null;
+  let call1Suggestions: Record<string, unknown> | null = null;
+  let error = '';
+  let busy = false;
+
+  async function checkReadiness() {
+    contentEnabled = false;
+    reachable = false;
+    try {
+      const [inf, test] = await Promise.all([
+        fetch('/api/v1/settings').then((r) => r.json()),
+        fetch('/api/v1/admin/test-inference', { method: 'POST' }).then((r) => r.json()),
+      ]);
+      contentEnabled = inf.content_llm_enabled === 'true' || inf.content_llm_enabled === true;
+      reachable = test.ok === true;
+    } catch {
+      reachable = false;
+    }
+  }
+
+  async function generate() {
+    if (!slabId) {
+      error = 'Enter a slab id.';
+      return;
+    }
+    busy = true;
+    error = '';
+    description = null;
+    try {
+      const res = await fetch(`/api/v1/slabs/${encodeURIComponent(slabId)}/inference/call2`, { method: 'POST' });
+      const body = await res.json();
+      if (res.ok) description = body.description;
+      else error = body.error?.message || `call2 failed (${res.status})`;
+    } catch {
+      error = 'network error';
+    }
+    busy = false;
+  }
+
+  async function classify() {
+    if (!slabId) {
+      error = 'Enter a slab id.';
+      return;
+    }
+    busy = true;
+    error = '';
+    call1Suggestions = null;
+    try {
+      const res = await fetch(`/api/v1/slabs/${encodeURIComponent(slabId)}/inference/call1`, { method: 'POST' });
+      const body = await res.json();
+      if (res.ok) call1Suggestions = body.suggestions;
+      else error = body.error?.message || `call1 failed (${res.status})`;
+    } catch {
+      error = 'network error';
+    }
+    busy = false;
+  }
+
+  checkReadiness();
+</script>
+
+<div class="inference">
+  <h2>Generate text</h2>
+  <p class="state">
+    Content generation: {contentEnabled ? 'on' : 'off'} · endpoint: {reachable ? 'reachable' : 'unreachable'}
+  </p>
+  {#if !contentEnabled || !reachable}
+    <p class="note">The Generate text control is disabled: it appears only when content generation is
+      enabled and the inference endpoint is reachable.</p>
+  {:else}
+    <div>
+      <label>Slab ID</label>
+      <input bind:value={slabId} placeholder="uuid" />
+    </div>
+    <div class="row">
+      <button on:click={generate} disabled={busy}>{busy ? 'Working…' : 'Generate description (Call 2)'}</button>
+      <button on:click={classify} disabled={busy}>Classify metadata (Call 1)</button>
+    </div>
+    {#if error}<p class="err">{error}</p>{/if}
+    {#if description}<p class="desc">{description}</p>{/if}
+    {#if call1Suggestions}
+      <pre class="sug">{JSON.stringify(call1Suggestions, null, 2)}</pre>
+    {/if}
+  {/if}
+  <button class="mini" on:click={checkReadiness}>Recheck readiness</button>
+</div>
+
+<style>
+  .inference { max-width: 560px; color: #eee; }
+  label { display: block; margin: 8px 0 4px; }
+  input { width: 100%; padding: 6px; }
+  .row { margin-top: 12px; display: flex; gap: 8px; }
+  .state { color: #aaa; }
+  .note { color: #e8a; }
+  .err { color: #e88; }
+  .desc { margin-top: 12px; }
+  .sug { background: #1c1c1c; padding: 8px; }
+  .mini { margin-top: 12px; font-size: 12px; }
+</style>