feat: Phase 3 V1 — Auto-Organization (domain_tags + valid_until)

Adds structural metadata that the LLM triage was already implicitly
reasoning about ("stale snapshot" → reject). Phase 3 captures that
reasoning as fields so it can DRIVE retrieval, not just rejection.

Schema (src/atocore/models/database.py):
- domain_tags TEXT DEFAULT '[]'  JSON array of lowercase topic keywords
- valid_until DATETIME            ISO date; null = permanent
- idx_memories_valid_until index for efficient expiry queries

Memory service (src/atocore/memory/service.py):
- Memory dataclass gains domain_tags + valid_until
- create_memory, update_memory accept/persist both
- _row_to_memory safely reads both (JSON-decode + null handling)
- _normalize_tags helper: lowercase, dedup, strip, cap at 10
- get_memories_for_context filters expired (valid_until < today UTC)
- _rank_memories_for_query adds tag-boost: memories whose domain_tags
  appear as substrings in query text rank higher (tertiary key after
  content-overlap density + absolute overlap, before confidence)

LLM extractor (_llm_prompt.py → llm-0.5.0):
- SYSTEM_PROMPT documents domain_tags (2-5 keywords) + valid_until
  (time-bounded facts get expiry dates; durable facts stay null)
- normalize_candidate_item parses both fields from model output with
  graceful fallback for string/null/missing

LLM triage (scripts/auto_triage.py):
- TRIAGE_SYSTEM_PROMPT documents same two fields
- parse_verdict extracts them from verdict JSON
- On promote: PUT /memory/{id} with tags + valid_until BEFORE
  POST /memory/{id}/promote, so active memories carry them

API (src/atocore/api/routes.py):
- MemoryCreateRequest: adds domain_tags, valid_until
- MemoryUpdateRequest: adds domain_tags, valid_until, memory_type
- GET /memory response exposes domain_tags + valid_until + created_at

Triage UI (src/atocore/engineering/triage_ui.py):
- Renders existing tags as colored badges
- Adds inline text field for tags (comma-separated) + date picker for
  valid_until on every candidate card
- Save&Promote button persists edits via PUT then promotes
- Plain Promote (and Y shortcut) also saves tags/expiry if edited

Wiki (src/atocore/engineering/wiki.py):
- Search now matches memory content OR domain_tags
- Search results render tags as clickable badges linking to
  /wiki/search?q=<tag> for cross-project navigation
- valid_until shown as amber "valid until YYYY-MM-DD" hint

Tests: 303 → 308 (5 new for Phase 3 behavior):
- test_create_memory_with_tags_and_valid_until
- test_create_memory_normalizes_tags
- test_update_memory_sets_tags_and_valid_until
- test_get_memories_for_context_excludes_expired
- test_context_builder_tag_boost_orders_results

Deferred (explicitly): temporal_scope enum, source_refs memory graph,
HDBSCAN clustering, memory detail wiki page, backfill of existing
actives. See docs/MASTER-BRAIN-PLAN.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/models/database.py

@@ -119,6 +119,23 @@ def _apply_migrations(conn: sqlite3.Connection) -> None:
         "CREATE INDEX IF NOT EXISTS idx_memories_last_referenced ON memories(last_referenced_at)"
     )
 
+    # Phase 3 (Auto-Organization V1): domain tags + expiry.
+    # domain_tags is a JSON array of lowercase strings (optics, mechanics,
+    # firmware, business, etc.) inferred by the LLM during triage. Used for
+    # cross-project retrieval: a query about "optics" can surface matches from
+    # p04 + p05 + p06 without knowing all the project names.
+    # valid_until is an ISO UTC timestamp beyond which the memory is
+    # considered stale. get_memories_for_context filters these out of context
+    # packs automatically so ephemeral facts (status snapshots, weekly counts)
+    # don't pollute grounding once they've aged out.
+    if not _column_exists(conn, "memories", "domain_tags"):
+        conn.execute("ALTER TABLE memories ADD COLUMN domain_tags TEXT DEFAULT '[]'")
+    if not _column_exists(conn, "memories", "valid_until"):
+        conn.execute("ALTER TABLE memories ADD COLUMN valid_until DATETIME")
+    conn.execute(
+        "CREATE INDEX IF NOT EXISTS idx_memories_valid_until ON memories(valid_until)"
+    )
+
     # Phase 9 Commit A: capture loop columns on the interactions table.
     # The original schema only carried prompt + project_id + a context_pack
     # JSON blob. To make interactions a real audit trail of what AtoCore fed