feat: content-hash-aware tag/insight sharing + library scoping

Tags and insights now follow content across libraries via content_hash
lookups on the read path, so the same file indexed at different rel_paths
in multiple libraries shares its annotations. Recursive tag search scopes
hits to the selected library by checking each tagged rel_path against
the library's disk (with a content-hash sibling fallback so tags attached
under one library's rel_path still match a content-equivalent file in
another). The /image and /image/metadata handlers fall back across
libraries when the file isn't under the resolved one, so union-mode
search results (which carry no library attribution in the response)
still serve correctly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/database/insights_dao.rs

@@ -21,6 +21,16 @@ pub trait InsightDao: Sync + Send {
         file_path: &str,
     ) -> Result<Option<PhotoInsight>, DbError>;
 
+    /// Return the most recent current insight whose rel_path is one of
+    /// `paths`. Used for content-hash sharing: the caller expands a
+    /// single file into all rel_paths with the same content_hash, then
+    /// asks here for any existing insight attached to any of them.
+    fn get_insight_for_paths(
+        &mut self,
+        context: &opentelemetry::Context,
+        paths: &[String],
+    ) -> Result<Option<PhotoInsight>, DbError>;
+
     fn get_insight_history(
         &mut self,
         context: &opentelemetry::Context,
@@ -132,6 +142,30 @@ impl InsightDao for SqliteInsightDao {
         .map_err(|_| DbError::new(DbErrorKind::QueryError))
     }
 
+    fn get_insight_for_paths(
+        &mut self,
+        context: &opentelemetry::Context,
+        paths: &[String],
+    ) -> Result<Option<PhotoInsight>, DbError> {
+        if paths.is_empty() {
+            return Ok(None);
+        }
+        trace_db_call(context, "query", "get_insight_for_paths", |_span| {
+            use schema::photo_insights::dsl::*;
+
+            let mut connection = self.connection.lock().expect("Unable to get InsightDao");
+
+            photo_insights
+                .filter(rel_path.eq_any(paths))
+                .filter(is_current.eq(true))
+                .order(generated_at.desc())
+                .first::<PhotoInsight>(connection.deref_mut())
+                .optional()
+                .map_err(|_| anyhow::anyhow!("Query error"))
+        })
+        .map_err(|_| DbError::new(DbErrorKind::QueryError))
+    }
+
     fn get_insight_history(
         &mut self,
         context: &opentelemetry::Context,