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/main.rs

@@ -67,6 +67,7 @@ mod tags;
 mod utils;
 mod video;
 
+mod knowledge;
 mod memories;
 mod otel;
 mod service;
@@ -1186,6 +1187,7 @@ fn main() -> std::io::Result<()> {
                 .service(ai::get_all_insights_handler)
                 .service(ai::get_available_models_handler)
                 .add_feature(add_tag_services::<_, SqliteTagDao>)
+                .add_feature(knowledge::add_knowledge_services::<_, SqliteKnowledgeDao>)
                 .app_data(app_data.clone())
                 .app_data::<Data<RealFileSystem>>(Data::new(RealFileSystem::new(
                     app_data.base_path.clone(),
@@ -1204,6 +1206,9 @@ fn main() -> std::io::Result<()> {
                 .app_data::<Data<Mutex<Box<dyn PreviewDao>>>>(Data::new(Mutex::new(Box::new(
                     preview_dao,
                 ))))
+                .app_data::<Data<Mutex<SqliteKnowledgeDao>>>(Data::new(Mutex::new(
+                    SqliteKnowledgeDao::new(),
+                )))
                 .app_data(web::JsonConfig::default().error_handler(|err, req| {
                     let detail = err.to_string();
                     log::warn!(