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/notifications.rs

@@ -1,5 +1,5 @@
-use tauri::command;
 use std::process::Command;
+use tauri::command;
 
 #[command]
 pub async fn send_notify_send(title: String, body: String) -> Result<(), String> {
@@ -10,7 +10,12 @@ pub async fn send_notify_send(title: String, body: String) -> Result<(), String>
         .arg("--urgency=normal")
         .arg("--app-name=Hikari Desktop")
         .output()
-        .map_err(|e| format!("Failed to execute notify-send: {}. Make sure libnotify-bin is installed.", e))?;
+        .map_err(|e| {
+            format!(
+                "Failed to execute notify-send: {}. Make sure libnotify-bin is installed.",
+                e
+            )
+        })?;
 
     if !output.status.success() {
         let error = String::from_utf8_lossy(&output.stderr);
@@ -93,4 +98,4 @@ pub async fn send_simple_notification(title: String, body: String) -> Result<(),
         .map_err(|e| format!("Failed to send message: {}", e))?;
 
     Ok(())
-}
+}