feat: new drafts feature and sound spam fix (#174)

## Summary

- **Saved Drafts feature**: Users can now save input content as drafts for later use, and manage them from a new panel
- **Sound spam fix**: The "Working on it!" sound no longer plays repeatedly when Claude makes multiple tool calls in a row

## Details

### Drafts feature
- Rust backend (`drafts.rs`) with `list_drafts`, `save_draft`, `delete_draft`, and `delete_all_drafts` commands, persisted to `hikari-drafts.json` via the Tauri Store plugin
- `draftsStore` wrapping all four commands with timestamp formatting
- `DraftPanel` overlay with insert, per-item two-step delete confirmation, delete-all with confirmation, empty state, and slide-in animation
- **Drafts** button in the top control row (pencil icon)
- **Save as Draft** floppy-disk icon button in the button wrapper (disabled when input is empty)

### Sound spam fix
- Root cause: `resetSoundState` was called on **every** `thinking` state transition, including mid-task transitions (`coding → thinking → coding`)
- Fix: only reset sound state when entering `thinking` from a clean-slate state (`idle`, `success`, or `error`) — states that genuinely mark the end of one task and the start of a new one

## Test plan
- [ ] Save a draft and verify it persists across app restarts
- [ ] Insert a draft and verify it populates the input
- [ ] Delete individual drafts and verify delete-all works
- [ ] Verify "Working on it!" plays once per user message regardless of how many tools are called

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #174
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src-tauri/src/lib.rs

@@ -6,6 +6,7 @@ mod config;
 mod cost_tracking;
 mod debug_logger;
 mod discord_rpc;
+mod drafts;
 mod git;
 mod notifications;
 mod process_ext;
@@ -28,6 +29,7 @@ use commands::load_saved_achievements;
 use commands::*;
 use debug_logger::TauriLogLayer;
 use discord_rpc::DiscordRpcManager;
+use drafts::*;
 use git::*;
 use notifications::*;
 use quick_actions::*;
@@ -214,6 +216,10 @@ pub fn run() {
             remove_mcp_server,
             add_mcp_server,
             get_mcp_server_details,
+            list_drafts,
+            save_draft,
+            delete_draft,
+            delete_all_drafts,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");