feat: era-rollup + narrative engine (consolidation steps 3-4)

Complete the consolidation pipeline: summaries -> profile + eras -> narrative.

- memory: eras table (per-month digests) + Era, summaries_by_month, store_era,
  list_eras, recall_eras; narrative table + set/get_narrative
- lyra/era.py (lyra-era): groups session gists by the month the session occurred
  (real timestamps) and map-reduces each month into a "what was happening" digest
- lyra/narrative.py (lyra-narrative): distills profile + recent eras into the
  current arc/trends/callbacks ("remember when…", "you're trending toward…")
- chat.build_messages injects the narrative alongside the profile

Verified on the real corpus: 17 monthly eras (Dec 2024-Jun 2026) + a narrative
that surfaces specific callbacks (the $573 Hollywood session, 4 years sober).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/chat.py

@@ -47,6 +47,13 @@ def build_messages(session_id: str, user_msg: str) -> list[Message]:
             {"role": "system", "content": "What you know about Brian:\n" + profile}
         )
 
+    # Time-aware memory: the current narrative (recent arc, trends, callbacks).
+    narrative = memory.get_narrative()
+    if narrative:
+        messages.append(
+            {"role": "system", "content": "What's going on with Brian lately:\n" + narrative}
+        )
+
     recent = memory.recent(session_id, n=RECENT_N)
     recent_ids = {ex.id for ex in recent}