- graph-memory.md: document temporal edge validity (valid_from/valid_until,
  edges_at_timestamp, edge_history, bfs_at_timestamp, temporal_decay_rate)
- providers.md: add Gemini Phase 4 SSE streaming tool use
- adaptive-inference.md: document cascade cost_tiers config
- observability.md: minor updates
- security/mcp.md: document tools/list_changed sanitization

Add a lightweight query classifier to zeph-memory that routes recall
queries to the optimal retrieval path based on temporal cues:

- Episodic queries (temporal keywords: "yesterday", "last week", etc.)
  route to SQLite FTS5 + optional created_at timestamp range filter
- Semantic queries continue through the existing BM25+RRF+MMR pipeline

Implementation details:
- `has_temporal_cue()`: word-boundary heuristic (no regex, no allocs)
  checked first in HeuristicRouter::route() before relationship patterns
- `strip_temporal_keywords()`: LazyLock sorted patterns, single-pass span
  removal, single lowercase allocation — ~18x fewer allocs vs naive impl
- `resolve_temporal_range(now)`: injectable clock for deterministic tests,
  covers 12 temporal expressions with explicit branches
- `keyword_search_with_time_range()`: parameterized sqlx queries, no
  schema changes, same access control predicates as existing path
- Add chrono `clock` feature to workspace dep for isolated crate builds

45 new tests: routing (temporal + false-positive guards), resolver
(deterministic with injected time), strip (edge cases + all-occurrence
removal), SQL filter (bounds, conversation isolation), Episodic dispatch
integration.