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/insights_dao.rs

@@ -21,6 +21,12 @@ pub trait InsightDao: Sync + Send {
         file_path: &str,
     ) -> Result<Option<PhotoInsight>, DbError>;
 
+    fn get_insight_history(
+        &mut self,
+        context: &opentelemetry::Context,
+        file_path: &str,
+    ) -> Result<Vec<PhotoInsight>, DbError>;
+
     fn delete_insight(
         &mut self,
         context: &opentelemetry::Context,
@@ -49,6 +55,11 @@ impl SqliteInsightDao {
             connection: Arc::new(Mutex::new(connect())),
         }
     }
+
+    #[cfg(test)]
+    pub fn from_connection(conn: Arc<Mutex<SqliteConnection>>) -> Self {
+        SqliteInsightDao { connection: conn }
+    }
 }
 
 impl InsightDao for SqliteInsightDao {
@@ -62,15 +73,22 @@ impl InsightDao for SqliteInsightDao {
 
             let mut connection = self.connection.lock().expect("Unable to get InsightDao");
 
-            // Insert or replace on conflict (UNIQUE constraint on file_path)
-            diesel::replace_into(photo_insights)
+            // Mark all existing insights for this file as no longer current
+            diesel::update(photo_insights.filter(file_path.eq(&insight.file_path)))
+                .set(is_current.eq(false))
+                .execute(connection.deref_mut())
+                .map_err(|_| anyhow::anyhow!("Update is_current error"))?;
+
+            // Insert the new insight as current
+            diesel::insert_into(photo_insights)
                 .values(&insight)
                 .execute(connection.deref_mut())
                 .map_err(|_| anyhow::anyhow!("Insert error"))?;
 
-            // Retrieve the inserted record
+            // Retrieve the inserted record (is_current = true)
             photo_insights
                 .filter(file_path.eq(&insight.file_path))
+                .filter(is_current.eq(true))
                 .first::<PhotoInsight>(connection.deref_mut())
                 .map_err(|_| anyhow::anyhow!("Query error"))
         })
@@ -89,6 +107,7 @@ impl InsightDao for SqliteInsightDao {
 
             photo_insights
                 .filter(file_path.eq(path))
+                .filter(is_current.eq(true))
                 .first::<PhotoInsight>(connection.deref_mut())
                 .optional()
                 .map_err(|_| anyhow::anyhow!("Query error"))
@@ -96,6 +115,25 @@ impl InsightDao for SqliteInsightDao {
         .map_err(|_| DbError::new(DbErrorKind::QueryError))
     }
 
+    fn get_insight_history(
+        &mut self,
+        context: &opentelemetry::Context,
+        path: &str,
+    ) -> Result<Vec<PhotoInsight>, DbError> {
+        trace_db_call(context, "query", "get_insight_history", |_span| {
+            use schema::photo_insights::dsl::*;
+
+            let mut connection = self.connection.lock().expect("Unable to get InsightDao");
+
+            photo_insights
+                .filter(file_path.eq(path))
+                .order(generated_at.desc())
+                .load::<PhotoInsight>(connection.deref_mut())
+                .map_err(|_| anyhow::anyhow!("Query error"))
+        })
+        .map_err(|_| DbError::new(DbErrorKind::QueryError))
+    }
+
     fn delete_insight(
         &mut self,
         context: &opentelemetry::Context,
@@ -124,6 +162,7 @@ impl InsightDao for SqliteInsightDao {
             let mut connection = self.connection.lock().expect("Unable to get InsightDao");
 
             photo_insights
+                .filter(is_current.eq(true))
                 .order(generated_at.desc())
                 .load::<PhotoInsight>(connection.deref_mut())
                 .map_err(|_| anyhow::anyhow!("Query error"))