feat: related-tags atlas in Explore view

Hovering a tag in Explore now loads and displays co-occurring tags as a
weighted cloud. New `get_related_tags` SQL self-join (db.rs/commands.rs),
`loadRelatedTags` store action with per-folder keyed cache, and TagCloud
atlas UI with ResizeObserver-driven layout and RAF animation. Explore tag
limit raised to 180; tag cloud auto-refreshes 700ms after new AI tagging
completes.

src-tauri/src/commands.rs

@@ -180,6 +180,19 @@ pub struct GetExploreTagsParams {
     pub limit: Option<usize>,
 }
 
+#[derive(Deserialize)]
+pub struct GetRelatedTagsParams {
+    pub tag: String,
+    pub folder_id: Option<i64>,
+    pub limit: Option<usize>,
+}
+
+#[derive(Serialize)]
+pub struct RelatedTagEntry {
+    pub tag: String,
+    pub shared_count: i64,
+}
+
 #[derive(Deserialize)]
 pub struct SearchTagsAutocompleteParams {
     pub query: String,
@@ -1277,7 +1290,28 @@ pub async fn get_explore_tags(
     params: GetExploreTagsParams,
 ) -> Result<Vec<ExploreTagEntry>, String> {
     let conn = db.get().map_err(|e| e.to_string())?;
-    db::get_explore_tags(&conn, params.folder_id, params.limit.unwrap_or(48))
+    db::get_explore_tags(&conn, params.folder_id, params.limit.unwrap_or(180))
+        .map_err(|e| e.to_string())
+}
+
+#[tauri::command]
+pub async fn get_related_tags(
+    db: State<'_, DbState>,
+    params: GetRelatedTagsParams,
+) -> Result<Vec<RelatedTagEntry>, String> {
+    let tag = params.tag.trim();
+    if tag.is_empty() {
+        return Ok(vec![]);
+    }
+
+    let conn = db.get().map_err(|e| e.to_string())?;
+    db::get_related_tags(&conn, tag, params.folder_id, params.limit.unwrap_or(16))
+        .map(|entries| {
+            entries
+                .into_iter()
+                .map(|(tag, shared_count)| RelatedTagEntry { tag, shared_count })
+                .collect()
+        })
         .map_err(|e| e.to_string())
 }
 

src-tauri/src/db.rs

@@ -2436,6 +2436,34 @@ pub fn get_explore_tags(
     Ok(rows)
 }
 
+pub fn get_related_tags(
+    conn: &Connection,
+    tag: &str,
+    folder_id: Option<i64>,
+    limit: usize,
+) -> Result<Vec<(String, i64)>> {
+    let mut stmt = conn.prepare(
+        "SELECT other.tag, COUNT(DISTINCT other.image_id) AS shared_count
+         FROM image_tags base
+         JOIN image_tags other ON other.image_id = base.image_id
+         JOIN images i ON i.id = base.image_id
+         WHERE base.tag = ?1
+           AND other.tag != base.tag
+           AND (?2 IS NULL OR i.folder_id = ?2)
+         GROUP BY other.tag
+         ORDER BY shared_count DESC, other.tag ASC
+         LIMIT ?3",
+    )?;
+
+    let rows = stmt
+        .query_map(params![tag, folder_id, limit as i64], |row| {
+            Ok((row.get::<_, String>(0)?, row.get::<_, i64>(1)?))
+        })?
+        .collect::<rusqlite::Result<Vec<_>>>()?;
+
+    Ok(rows)
+}
+
 type FailedEmbeddingRow = (i64, String, String, Option<String>);
 
 pub fn get_failed_embedding_images(

src-tauri/src/lib.rs

@@ -197,6 +197,7 @@ pub fn run() {
             commands::get_worker_states,
             commands::get_tag_cloud,
             commands::get_explore_tags,
+            commands::get_related_tags,
             commands::get_images_by_ids,
             commands::get_failed_embedding_images,
             commands::get_failed_tagging_images,