feat: add font size and zoom settings

- Add font_size config field (10-24px, default 14px)
- Add keyboard shortcuts: Ctrl++/- to adjust, Ctrl+0 to reset
- Add font size slider in Settings > Appearance
- Apply font size to Terminal and InputBar via CSS variable
- Persist font size preference between sessions

Closes #19

src/routes/+page.svelte

@@ -3,7 +3,7 @@
   import { invoke } from "@tauri-apps/api/core";
   import { get } from "svelte/store";
   import { initializeTauriListeners, cleanupTauriListeners } from "$lib/tauri";
-  import { configStore, applyTheme } from "$lib/stores/config";
+  import { configStore, applyTheme, applyFontSize } from "$lib/stores/config";
   import { initNotificationSync, cleanupNotificationSync } from "$lib/stores/notifications";
   import { conversationsStore } from "$lib/stores/conversations";
   import { claudeStore, isClaudeProcessing } from "$lib/stores/claude";
@@ -100,6 +100,27 @@
         return;
       }
     }
+
+    // Ctrl++ or Ctrl+= - Increase font size
+    if (event.ctrlKey && (event.key === "+" || event.key === "=")) {
+      event.preventDefault();
+      configStore.increaseFontSize();
+      return;
+    }
+
+    // Ctrl+- - Decrease font size
+    if (event.ctrlKey && event.key === "-") {
+      event.preventDefault();
+      configStore.decreaseFontSize();
+      return;
+    }
+
+    // Ctrl+0 - Reset font size
+    if (event.ctrlKey && event.key === "0") {
+      event.preventDefault();
+      configStore.resetFontSize();
+      return;
+    }
   }
 
   async function handleInterrupt() {
@@ -127,6 +148,7 @@
       // Apply saved settings on startup
       const config = configStore.getConfig();
       applyTheme(config.theme);
+      applyFontSize(config.font_size);
 
       // Apply always-on-top setting
       if (config.always_on_top) {