feat: add entity-relationship knowledge memory to agentic insights

Implements persistent cross-photo knowledge memory so the agentic
insight loop can learn and recall facts about people, places, and
events across the photo collection.

Changes:
- photo_insights: drop UNIQUE(file_path) + INSERT OR REPLACE, replace
  with append-only rows + is_current flag for insight history retention
- New tables: entities, entity_facts, entity_photo_links with FK
  constraints and confidence scoring
- KnowledgeDao trait + SqliteKnowledgeDao with upsert, merge, and
  corroboration (confidence +0.1 on duplicate fact detection)
- Four new agent tools: recall_entities, recall_facts_for_photo,
  store_entity, store_fact (with object_entity_id FK support)
- Cameron entity auto-seeded with stable ID injected into system prompt
- Pre-run photo link clearing + post-loop source_insight_id backfill
- Audit REST API: GET/PATCH/DELETE /knowledge/entities/{id},
  POST /knowledge/entities/merge, GET/PATCH/DELETE /knowledge/facts/{id},
  GET /knowledge/recent

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/database/mod.rs

@@ -12,6 +12,7 @@ use crate::otel::trace_db_call;
 pub mod calendar_dao;
 pub mod daily_summary_dao;
 pub mod insights_dao;
+pub mod knowledge_dao;
 pub mod location_dao;
 pub mod models;
 pub mod preview_dao;
@@ -21,6 +22,10 @@ pub mod search_dao;
 pub use calendar_dao::{CalendarEventDao, SqliteCalendarEventDao};
 pub use daily_summary_dao::{DailySummaryDao, InsertDailySummary, SqliteDailySummaryDao};
 pub use insights_dao::{InsightDao, SqliteInsightDao};
+pub use knowledge_dao::{
+    EntityFilter, EntityPatch, FactFilter, FactPatch, KnowledgeDao, RecentActivity,
+    SqliteKnowledgeDao,
+};
 pub use location_dao::{LocationHistoryDao, SqliteLocationHistoryDao};
 pub use preview_dao::{PreviewDao, SqlitePreviewDao};
 pub use search_dao::{SearchHistoryDao, SqliteSearchHistoryDao};