feat: cloud-first consolidation routing + graceful backend fallback

Nail down which backend each LLM path uses, and make the dream cycle resilient to
a backend being down (the MI50 outage left profile/era/narrative — pinned to mi50
with no fallback — aborting every dream cycle).

- Consolidation (summaries + profile/era/narrative) -> cloud via SUMMARY_BACKEND=
  cloud (.env, not committed). Matches the documented lesson that the MI50 is too
  slow/hot for bulk consolidation; nothing background touches the card now.
- llm.complete_with_fallback(): try the primary backend, fall back to cloud on
  error (re-raise if already cloud / no key). Wired into reflect + think so the
  introspection voice (3090/dolphin) survives the gaming PC being powered off.
- dream coherence stage is now fault-isolated: a rebuild failure logs + continues
  instead of sinking the whole pass (reflection still runs).
- .env: removed stale INTROSPECTION_BACKEND=mi50 (live routing is the web-switchable
  introspection_mode DB setting = dolphin/3090; the var only fed a dead fallback).

Verified: forced cycle runs consolidation on cloud, introspection on the 3090,
completes with zero MI50 calls. 206 pass, ruff clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015yrEb5qpPGv2FjyxrB7LLk

tests/test_thoughts.py

@@ -31,7 +31,7 @@ def lyra(tmp_path, monkeypatch):
     # Canned LLM: tests set `box["next"]` to the dict think() should "generate".
     box = {"next": {}}
     monkeypatch.setattr(thoughts.llm, "complete",
-                        lambda messages, backend=None, model=None: json.dumps(box["next"]))
+                        lambda messages, backend=None, model=None, **_: json.dumps(box["next"]))
     # Keep the loop offline + silent by default: no feed fetch, no push.
     monkeypatch.setattr(thoughts.feeds, "next_item", lambda **k: None)
     monkeypatch.setattr(thoughts.notify, "push", lambda **k: False)
@@ -342,7 +342,7 @@ def test_think_routes_to_selected_voice(lyra, monkeypatch):
     self_state.set_introspection_mode("dolphin")
     seen = {}
 
-    def cap(messages, backend="local", model=None):
+    def cap(messages, backend="local", model=None, **_):
         seen["backend"], seen["model"] = backend, model
         return json.dumps(box["next"])