feat(kon): add storage crate — SQLite schema, CRUD operations

- SQLite via sqlx 0.8 with runtime-tokio
- Schema: transcripts, segments, tasks, task_lists, settings tables
- Full CRUD for transcripts (insert, get, list, delete)
- Full CRUD for tasks (insert, list, complete, delete)
- Settings key-value store (insert/replace, get)
- File storage paths: app_data_dir, database_path, recordings_dir
- 3 async tests passing against in-memory SQLite, clippy clean

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

crates/storage/src/file_storage.rs

@@ -0,0 +1,26 @@
+use std::path::PathBuf;
+
+/// Resolve the app data directory.
+/// Windows: %LOCALAPPDATA%/kon
+/// Unix: ~/.kon
+pub fn app_data_dir() -> PathBuf {
+    if cfg!(target_os = "windows") {
+        let local_app_data =
+            std::env::var("LOCALAPPDATA").unwrap_or_else(|_| ".".to_string());
+        PathBuf::from(local_app_data).join("kon")
+    } else {
+        let home =
+            std::env::var("HOME").unwrap_or_else(|_| "/tmp".to_string());
+        PathBuf::from(home).join(".kon")
+    }
+}
+
+/// Path to the SQLite database file.
+pub fn database_path() -> PathBuf {
+    app_data_dir().join("kon.db")
+}
+
+/// Directory for saved audio recordings.
+pub fn recordings_dir() -> PathBuf {
+    app_data_dir().join("recordings")
+}