Architect agent: Claude-powered thesis generation (backend scaffolding)

- backend/mcp/architect_agent.py: generate_options + revise on Claude (prompt-
  cached thesis context, claude-opus-4-8, Ten31 voice rules). Writes N variant
  drafts to a node's variant group; nothing canonical without human approval.
  Fails gracefully if the API key / SDK is absent.
- server.py endpoints: GET /api/architect/status, GET /api/thesis/{key}/tree,
  GET /api/thesis/nodes/{id}/variants, POST .../generate, POST .../feedback,
  POST /api/thesis/lines, POST /api/thesis/lines/{key}/nodes. architect_tools
  gains get_node_variants.
- Dockerfile installs `anthropic`; docker_entrypoint loads ANTHROPIC_API_KEY from
  /data/secrets/anthropic-api-key (self-disabling until the key is dropped in).

Full HTTP surface verified end-to-end (graceful 502 without a key).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/mcp/architect_tools.py

@@ -95,6 +95,23 @@ def get_node(node_id, db=None):
     return dict(r) if r else {"error": "not_found", "node_id": node_id}
 
 
+def get_node_variants(node_id, db=None):
+    """All competing options for a node (its variant group). The number is fluid:
+    a node may have one option or many at any moment."""
+    c = _conn(db)
+    node = c.execute("SELECT line_id, variant_group, node_type, title FROM thesis_nodes WHERE id=?", (node_id,)).fetchone()
+    if not node:
+        c.close()
+        return {"error": "not_found", "node_id": node_id}
+    group = node["variant_group"] or node_id
+    rows = [dict(r) for r in c.execute(
+        "SELECT id, body, title, status, variant_group, meta FROM thesis_nodes "
+        "WHERE (variant_group=? OR id=?) AND deleted_at IS NULL ORDER BY created_at", (group, node_id))]
+    c.close()
+    return {"node_id": node_id, "variant_group": group, "node_type": node["node_type"],
+            "title": node["title"], "variants": rows}
+
+
 def get_node_history(node_id, db=None):
     c = _conn(db)
     rows = [dict(r) for r in c.execute(