Add tags, export/import, and changelog features

- Tag editor in detail view with add/remove pill chips
- Tag filter chips in library view for filtering by tag
- Shared backup module for app list export/import (JSON v2)
- CLI export/import refactored to use shared module
- GUI export/import via file picker dialogs in hamburger menu
- GitHub release history enrichment for catalog apps
- Changelog preview in updates view with expandable rows
- DB migration v19 for catalog release_history column

src/core/database.rs

@@ -154,6 +154,7 @@ pub struct CatalogApp {
     pub ocs_arch: Option<String>,
     pub ocs_md5sum: Option<String>,
     pub ocs_comments: Option<i64>,
+    pub release_history: Option<String>,
 }
 
 #[derive(Debug, Clone)]
@@ -484,6 +485,10 @@ impl Database {
             self.migrate_to_v18()?;
         }
 
+        if current_version < 19 {
+            self.migrate_to_v19()?;
+        }
+
         // Ensure all expected columns exist (repairs DBs where a migration
         // was updated after it had already run on this database)
         self.ensure_columns()?;
@@ -1050,6 +1055,18 @@ impl Database {
         Ok(())
     }
 
+    fn migrate_to_v19(&self) -> SqlResult<()> {
+        self.conn.execute(
+            "ALTER TABLE catalog_apps ADD COLUMN release_history TEXT",
+            [],
+        ).ok();
+        self.conn.execute(
+            "UPDATE schema_version SET version = ?1",
+            params![19],
+        )?;
+        Ok(())
+    }
+
     pub fn upsert_appimage(
         &self,
         path: &str,
@@ -1221,7 +1238,8 @@ impl Database {
          github_enriched_at, github_download_url, github_release_assets, github_description, github_readme,
          ocs_id, ocs_downloads, ocs_score, ocs_typename, ocs_personid, ocs_description, ocs_summary,
          ocs_version, ocs_tags, ocs_changed, ocs_preview_url,
-         ocs_detailpage, ocs_created, ocs_downloadname, ocs_downloadsize, ocs_arch, ocs_md5sum, ocs_comments";
+         ocs_detailpage, ocs_created, ocs_downloadname, ocs_downloadsize, ocs_arch, ocs_md5sum, ocs_comments,
+         release_history";
 
     /// SQL filter that deduplicates catalog apps by lowercase name.
     /// Keeps the OCS entry when both OCS and secondary source entries exist for the same name.
@@ -1277,6 +1295,7 @@ impl Database {
             ocs_arch: row.get(35).unwrap_or(None),
             ocs_md5sum: row.get(36).unwrap_or(None),
             ocs_comments: row.get(37).unwrap_or(None),
+            release_history: row.get(38).unwrap_or(None),
         })
     }
 
@@ -2066,6 +2085,27 @@ impl Database {
         Ok(())
     }
 
+    /// Get all distinct tags used across all installed apps.
+    /// Returns a sorted, deduplicated list of tag strings.
+    pub fn get_all_tags(&self) -> SqlResult<Vec<String>> {
+        let mut stmt = self.conn.prepare(
+            "SELECT tags FROM appimages WHERE tags IS NOT NULL AND tags != ''"
+        )?;
+        let rows = stmt.query_map([], |row| row.get::<_, String>(0))?;
+        let mut tag_set = std::collections::BTreeSet::new();
+        for row in rows {
+            if let Ok(tags_str) = row {
+                for tag in tags_str.split(',') {
+                    let trimmed = tag.trim();
+                    if !trimmed.is_empty() {
+                        tag_set.insert(trimmed.to_string());
+                    }
+                }
+            }
+        }
+        Ok(tag_set.into_iter().collect())
+    }
+
     pub fn set_pinned(&self, id: i64, pinned: bool) -> SqlResult<()> {
         self.conn.execute(
             "UPDATE appimages SET pinned = ?2 WHERE id = ?1",
@@ -2479,6 +2519,23 @@ impl Database {
         }
     }
 
+    /// Look up release history from catalog for an installed app (by name).
+    /// Returns the release_history JSON string if a matching catalog app has one.
+    pub fn get_catalog_release_history_by_name(&self, app_name: &str) -> SqlResult<Option<String>> {
+        let result = self.conn.query_row(
+            "SELECT release_history FROM catalog_apps
+             WHERE LOWER(name) = LOWER(?1) AND release_history IS NOT NULL
+             LIMIT 1",
+            params![app_name],
+            |row| row.get::<_, Option<String>>(0),
+        );
+        match result {
+            Ok(history) => Ok(history),
+            Err(rusqlite::Error::QueryReturnedNoRows) => Ok(None),
+            Err(e) => Err(e),
+        }
+    }
+
     /// Get featured catalog apps. Apps with enrichment data (stars or OCS downloads)
     /// sort first by combined popularity, then unenriched apps get a deterministic
     /// shuffle that rotates every 15 minutes.
@@ -2860,6 +2917,18 @@ impl Database {
         )?;
         Ok(())
     }
+
+    pub fn update_catalog_app_release_history(
+        &self,
+        app_id: i64,
+        history_json: &str,
+    ) -> SqlResult<()> {
+        self.conn.execute(
+            "UPDATE catalog_apps SET release_history = ?2 WHERE id = ?1",
+            params![app_id, history_json],
+        )?;
+        Ok(())
+    }
 }
 
 #[cfg(test)]