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/lib/stores/conversations.ts

@@ -21,6 +21,7 @@ export interface Conversation {
   grantedTools: Set<string>;
   pendingPermission: PermissionRequest | null;
   pendingQuestion: UserQuestionEvent | null;
+  scrollPosition: number;
   createdAt: Date;
   lastActivityAt: Date;
 }
@@ -55,6 +56,7 @@ function createConversationsStore() {
       grantedTools: new Set(),
       pendingPermission: null,
       pendingQuestion: null,
+      scrollPosition: -1, // -1 means "scroll to bottom" (auto-scroll)
       createdAt: new Date(),
       lastActivityAt: new Date(),
     };
@@ -106,6 +108,7 @@ function createConversationsStore() {
     ($conv) => $conv?.pendingPermission || null
   );
   const pendingQuestion = derived(activeConversation, ($conv) => $conv?.pendingQuestion || null);
+  const scrollPosition = derived(activeConversation, ($conv) => $conv?.scrollPosition ?? -1);
 
   return {
     // Expose derived stores for compatibility
@@ -118,6 +121,7 @@ function createConversationsStore() {
     isProcessing: { subscribe: isProcessing.subscribe },
     grantedTools: { subscribe: grantedTools.subscribe },
     pendingRetryMessage: { subscribe: pendingRetryMessage.subscribe },
+    scrollPosition: { subscribe: scrollPosition.subscribe },
 
     // New conversation-specific stores
     conversations: { subscribe: conversations.subscribe },
@@ -325,6 +329,22 @@ function createConversationsStore() {
       });
     },
 
+    saveScrollPosition: (id: string, position: number) => {
+      conversations.update((convs) => {
+        const conv = convs.get(id);
+        if (conv) {
+          conv.scrollPosition = position;
+        }
+        return convs;
+      });
+    },
+
+    getScrollPosition: (id: string): number => {
+      const convs = get(conversations);
+      const conv = convs.get(id);
+      return conv?.scrollPosition ?? -1;
+    },
+
     // Methods that operate on the active conversation
     setSessionId: (id: string | null) => {
       ensureInitialized();