feat: another wave of features (#61)

## Explanation

This PR bundles several user-facing improvements and feature additions for the v0.3.0 release, including quality-of-life improvements to the UI, new slash commands, better state persistence, and auto-update checking.

## Included Changes

- **Resizable chat input** with drag handle (#58 partial)
- **Arrow key navigation fix** - cursor keys now navigate text when user has typed input (#58)
- **Scroll position persistence** per conversation tab
- **/skill command** for invoking Claude Code skills (#57)
- **Stats persistence fix** - stats now persist across session changes, only reset on disconnect (#59)
- **Auto-update checker** on startup (#17)
- **Resizable character panel** with full-height sprites (#10)
- **Font size and zoom settings** with keyboard shortcuts (Ctrl++/Ctrl+-/Ctrl+0) (#19)

## Closes

Closes #10, #17, #19, #57, #58, #59

## Attestations

- [x] I have read and agree to the Code of Conduct
- [x] I have read and agree to the Community Guidelines
- [x] My contribution complies with the Contributor Covenant
- [x] I have run the linter and resolved any errors
- [x] My pull request uses an appropriate title, matching the conventional commit standards
- [x] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request
- [x] All new and existing tests pass locally with my changes
- [x] Code coverage remains at or above the configured threshold

## Documentation

N/A - Internal app features

## Versioning

Minor - My pull request introduces new non-breaking features.

---
✨ This PR was created with help from Hikari~ 🌸

Co-authored-by: Hikari <hikari@nhcarrigan.com>
Reviewed-on: #61
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/windows_toast.rs

@@ -2,7 +2,7 @@ use tauri::command;
 
 #[cfg(target_os = "windows")]
 use windows::{
-    core::{HSTRING, Result as WindowsResult},
+    core::{Result as WindowsResult, HSTRING},
     Data::Xml::Dom::*,
     UI::Notifications::*,
 };
@@ -38,7 +38,8 @@ fn show_toast_notification(title: &str, body: &str) -> WindowsResult<()> {
     let toast = ToastNotification::CreateToastNotification(&xml_doc)?;
 
     // Create a toast notifier with an application ID
-    let notifier = ToastNotificationManager::CreateToastNotifierWithId(&HSTRING::from("Hikari Desktop"))?;
+    let notifier =
+        ToastNotificationManager::CreateToastNotifierWithId(&HSTRING::from("Hikari Desktop"))?;
 
     // Show the notification
     notifier.Show(&toast)?;
@@ -60,4 +61,4 @@ fn escape_xml(text: &str) -> String {
 #[command]
 pub async fn send_windows_toast(_title: String, _body: String) -> Result<(), String> {
     Err("Windows toast notifications are only available on Windows".to_string())
-}
+}