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/schema.rs

@@ -31,6 +31,44 @@ diesel::table! {
     }
 }
 
+diesel::table! {
+    entities (id) {
+        id -> Integer,
+        name -> Text,
+        entity_type -> Text,
+        description -> Text,
+        embedding -> Nullable<Binary>,
+        confidence -> Float,
+        status -> Text,
+        created_at -> BigInt,
+        updated_at -> BigInt,
+    }
+}
+
+diesel::table! {
+    entity_facts (id) {
+        id -> Integer,
+        subject_entity_id -> Integer,
+        predicate -> Text,
+        object_entity_id -> Nullable<Integer>,
+        object_value -> Nullable<Text>,
+        source_photo -> Nullable<Text>,
+        source_insight_id -> Nullable<Integer>,
+        confidence -> Float,
+        status -> Text,
+        created_at -> BigInt,
+    }
+}
+
+diesel::table! {
+    entity_photo_links (id) {
+        id -> Integer,
+        entity_id -> Integer,
+        file_path -> Text,
+        role -> Text,
+    }
+}
+
 diesel::table! {
     favorites (id) {
         id -> Integer,
@@ -112,6 +150,7 @@ diesel::table! {
         summary -> Text,
         generated_at -> BigInt,
         model_version -> Text,
+        is_current -> Bool,
     }
 }
 
@@ -165,11 +204,16 @@ diesel::table! {
     }
 }
 
+diesel::joinable!(entity_facts -> photo_insights (source_insight_id));
+diesel::joinable!(entity_photo_links -> entities (entity_id));
 diesel::joinable!(tagged_photo -> tags (tag_id));
 
 diesel::allow_tables_to_appear_in_same_query!(
     calendar_events,
     daily_conversation_summaries,
+    entities,
+    entity_facts,
+    entity_photo_links,
     favorites,
     image_exif,
     knowledge_embeddings,