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/lib.rs

@@ -2,8 +2,8 @@ pub mod database;
 pub mod file_storage;
 
 pub use database::{
-    complete_task, delete_task, delete_transcript, get_setting, get_transcript,
-    init, insert_task, insert_transcript, list_tasks, list_transcripts,
-    log_error, set_setting, InsertTranscriptParams, TaskRow, TranscriptRow,
+    complete_task, delete_task, delete_transcript, get_setting, get_transcript, init, insert_task,
+    insert_transcript, list_tasks, list_transcripts, log_error, set_setting,
+    InsertTranscriptParams, TaskRow, TranscriptRow,
 };
 pub use file_storage::{app_data_dir, database_path, recordings_dir};