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/stats.rs

@@ -1,7 +1,7 @@
+use crate::achievements::{check_achievements, AchievementProgress};
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::time::Instant;
-use crate::achievements::{AchievementProgress, check_achievements};
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
 pub struct UsageStats {
@@ -89,7 +89,10 @@ impl UsageStats {
 
     pub fn increment_tool_usage(&mut self, tool_name: &str) {
         *self.tools_usage.entry(tool_name.to_string()).or_insert(0) += 1;
-        *self.session_tools_usage.entry(tool_name.to_string()).or_insert(0) += 1;
+        *self
+            .session_tools_usage
+            .entry(tool_name.to_string())
+            .or_insert(0) += 1;
     }
 
     pub fn get_session_duration(&mut self) -> u64 {
@@ -213,4 +216,4 @@ mod tests {
         assert_eq!(stats.session_cost_usd, 0.0);
         assert!(stats.total_cost_usd > 0.0);
     }
-}
+}