refactor(kon): clean up storage and cloud-providers — remove unused deps, add safety docs

- Remove unused chrono and uuid dependencies from kon-storage
- Add schema versioning TODO to run_migrations() for pre-release safety
- Add doc comment and usage example to log_error() (uncalled public API)
- Add TODO to consolidate app_data_dir() with model_manager::dirs_path()
- Add safety comments and #[allow(deprecated)] to keystore set_var usage
- Add TODO for keyring crate migration in cloud-providers keystore
- Apply cargo fmt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/storage/src/database.rs

@@ -27,6 +27,11 @@ pub async fn init(db_path: &Path) -> Result<SqlitePool> {
 }
 
 /// Run schema migrations.
+///
+/// TODO(pre-release): Implement schema versioning for safe upgrades.
+/// Currently uses `CREATE TABLE IF NOT EXISTS` which silently ignores column
+/// additions/removals. Before shipping, add a `schema_version` table and
+/// sequential migration steps so existing user databases upgrade cleanly.
 async fn run_migrations(pool: &SqlitePool) -> Result<()> {
     sqlx::query(
         "CREATE TABLE IF NOT EXISTS transcripts (
@@ -186,10 +191,7 @@ pub async fn insert_transcript(
     Ok(())
 }
 
-pub async fn get_transcript(
-    pool: &SqlitePool,
-    id: &str,
-) -> Result<Option<TranscriptRow>> {
+pub async fn get_transcript(pool: &SqlitePool, id: &str) -> Result<Option<TranscriptRow>> {
     let row = sqlx::query(
         "SELECT id, text, source, title, audio_path, duration, engine, model_id, inference_ms, sample_rate, audio_channels, format_mode, remove_fillers, british_english, anti_hallucination, created_at FROM transcripts WHERE id = ?",
     )
@@ -231,16 +233,14 @@ pub async fn insert_task(
     bucket: &str,
     source_transcript_id: Option<&str>,
 ) -> Result<()> {
-    sqlx::query(
-        "INSERT INTO tasks (id, text, bucket, source_transcript_id) VALUES (?, ?, ?, ?)",
-    )
-    .bind(id)
-    .bind(text)
-    .bind(bucket)
-    .bind(source_transcript_id)
-    .execute(pool)
-    .await
-    .map_err(|e| KonError::StorageError(format!("Insert task failed: {e}")))?;
+    sqlx::query("INSERT INTO tasks (id, text, bucket, source_transcript_id) VALUES (?, ?, ?, ?)")
+        .bind(id)
+        .bind(text)
+        .bind(bucket)
+        .bind(source_transcript_id)
+        .execute(pool)
+        .await
+        .map_err(|e| KonError::StorageError(format!("Insert task failed: {e}")))?;
     Ok(())
 }
 
@@ -364,7 +364,19 @@ fn transcript_row_from(r: &sqlx::sqlite::SqliteRow) -> TranscriptRow {
 
 // --- Error Logging ---
 
-/// Log a structured error to the error_log table.
+/// Log a structured error to the `error_log` table.
+///
+/// Available for Tauri command handlers to persist errors for diagnostics.
+/// Each entry records context (which subsystem), an optional error code,
+/// the human-readable message, and optional JSON metadata.
+///
+/// # Example
+/// ```ignore
+/// log_error(&pool, "transcription", Some("WHISPER_INIT"), "Model load failed", None).await?;
+/// ```
+///
+/// TODO: Wire this into Tauri command error paths so runtime failures are
+/// persisted for user-facing error history and crash diagnostics.
 pub async fn log_error(
     pool: &SqlitePool,
     context: &str,