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>

migrations/2026-04-02-000100_add_knowledge_memory/down.sql

@@ -0,0 +1,3 @@
+DROP TABLE IF EXISTS entity_photo_links;
+DROP TABLE IF EXISTS entity_facts;
+DROP TABLE IF EXISTS entities;

migrations/2026-04-02-000100_add_knowledge_memory/up.sql

@@ -0,0 +1,55 @@
+-- Entity-relationship knowledge memory tables.
+-- Entities are the nodes (people, places, events, things).
+-- entity_facts are typed claims about or between entities.
+-- entity_photo_links connect entities to specific photos.
+
+CREATE TABLE entities (
+    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+    name TEXT NOT NULL,
+    entity_type TEXT NOT NULL,          -- 'person' | 'place' | 'event' | 'thing'
+    description TEXT NOT NULL DEFAULT '',
+    embedding BLOB,                     -- 768-dim f32 vector; nullable if embedding service was unavailable
+    confidence REAL NOT NULL DEFAULT 0.5,
+    status TEXT NOT NULL DEFAULT 'active',  -- 'active' | 'reviewed' | 'rejected'
+    created_at BIGINT NOT NULL,
+    updated_at BIGINT NOT NULL,
+    UNIQUE(name, entity_type)
+);
+
+CREATE INDEX idx_entities_type ON entities(entity_type);
+CREATE INDEX idx_entities_status ON entities(status);
+CREATE INDEX idx_entities_name ON entities(name);
+
+CREATE TABLE entity_facts (
+    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+    subject_entity_id INTEGER NOT NULL,
+    predicate TEXT NOT NULL,
+    object_entity_id INTEGER,           -- nullable: entity-to-entity relationship target
+    object_value TEXT,                  -- nullable: free-text attribute value
+    source_photo TEXT,                  -- photo path that prompted extraction (injected server-side)
+    source_insight_id INTEGER,          -- backfilled after insight is stored
+    confidence REAL NOT NULL DEFAULT 0.6,
+    status TEXT NOT NULL DEFAULT 'active',  -- 'active' | 'reviewed' | 'rejected'
+    created_at BIGINT NOT NULL,
+    CONSTRAINT fk_ef_subject FOREIGN KEY (subject_entity_id) REFERENCES entities(id) ON DELETE CASCADE,
+    CONSTRAINT fk_ef_object  FOREIGN KEY (object_entity_id)  REFERENCES entities(id) ON DELETE SET NULL,
+    CONSTRAINT fk_ef_insight FOREIGN KEY (source_insight_id) REFERENCES photo_insights(id) ON DELETE SET NULL,
+    CHECK (object_entity_id IS NOT NULL OR object_value IS NOT NULL)
+);
+
+CREATE INDEX idx_entity_facts_subject ON entity_facts(subject_entity_id);
+CREATE INDEX idx_entity_facts_predicate ON entity_facts(predicate);
+CREATE INDEX idx_entity_facts_status ON entity_facts(status);
+CREATE INDEX idx_entity_facts_source_photo ON entity_facts(source_photo);
+
+CREATE TABLE entity_photo_links (
+    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+    entity_id INTEGER NOT NULL,
+    file_path TEXT NOT NULL,
+    role TEXT NOT NULL,                 -- 'subject' | 'location' | 'event' | 'thing'
+    CONSTRAINT fk_epl_entity FOREIGN KEY (entity_id) REFERENCES entities(id) ON DELETE CASCADE,
+    UNIQUE(entity_id, file_path, role)
+);
+
+CREATE INDEX idx_entity_photo_links_entity ON entity_photo_links(entity_id);
+CREATE INDEX idx_entity_photo_links_photo ON entity_photo_links(file_path);