feat(appearance): apply UI zoom level to terminal and Monaco editors

Extend the existing appearance zoom setting so it also scales xterm.js
terminals and Monaco editors (diff viewer, three-pane merge editor, file
workspace editor), which previously rendered at a hard-coded 13px
regardless of zoom.

- Terminals read zoom at init and update term.options.fontSize live on
  zoom change, refitting after a double rAF so xterm's renderer has
  recomputed cell metrics. Font size is rounded to an integer to avoid
  subpixel blur in the canvas renderer.
- Monaco editors derive fontSize from zoomLevel; three-pane merge
  editor memoizes its options object to avoid redundant updateOptions
  calls on unrelated re-renders.

src/components/terminal/terminal-view.tsx

@@ -8,8 +8,15 @@ import {
   terminalResize,
   terminalKill,
 } from "@/lib/api"
+import { useZoomLevel } from "@/hooks/use-appearance"
 import type { TerminalEvent } from "@/lib/types"
-import type { ITheme } from "@xterm/xterm"
+import type { ITheme, Terminal as XTermTerminal } from "@xterm/xterm"
+
+const TERMINAL_BASE_FONT_SIZE = 13
+
+function computeTerminalFontSize(zoomLevel: number): number {
+  return Math.round((TERMINAL_BASE_FONT_SIZE * zoomLevel) / 100)
+}
 
 const DARK_THEME: ITheme = {
   background: "#1a1a1a",
@@ -108,11 +115,13 @@ export function TerminalView({
 }: TerminalViewProps) {
   const containerRef = useRef<HTMLDivElement>(null)
   const fitAddonRef = useRef<{ fit: () => void } | null>(null)
-  const termRef = useRef<{ focus: () => void } | null>(null)
+  const termRef = useRef<XTermTerminal | null>(null)
   const lastResizeRef = useRef<{ cols: number; rows: number } | null>(null)
   const isActiveRef = useRef(isActive)
   const isVisibleRef = useRef(isVisible)
   const onProcessExitedRef = useRef(onProcessExited)
+  const { zoomLevel } = useZoomLevel()
+  const zoomLevelRef = useRef(zoomLevel)
   const [loading, setLoading] = useState(true)
 
   useEffect(() => {
@@ -140,7 +149,7 @@ export function TerminalView({
 
       const term = new Terminal({
         cursorBlink: true,
-        fontSize: 13,
+        fontSize: computeTerminalFontSize(zoomLevelRef.current),
         fontFamily: "Menlo, Monaco, 'Courier New', monospace",
         theme: getTerminalTheme(containerRef.current),
         allowProposedApi: true,
@@ -292,6 +301,25 @@ export function TerminalView({
     }
   }, [isActive, isVisible])
 
+  // React to zoom level changes. Updates the ref synchronously so async init()
+  // always reads the latest zoom, and pushes the new font size to already-mounted
+  // terminals. Double rAF ensures xterm's renderer has recomputed cell metrics
+  // before we refit.
+  useEffect(() => {
+    zoomLevelRef.current = zoomLevel
+    const term = termRef.current
+    if (!term) return
+    term.options.fontSize = computeTerminalFontSize(zoomLevel)
+    requestAnimationFrame(() => {
+      requestAnimationFrame(() => {
+        const el = containerRef.current
+        if (el && el.clientWidth > 0 && el.clientHeight > 0) {
+          fitAddonRef.current?.fit()
+        }
+      })
+    })
+  }, [zoomLevel])
+
   return (
     <div
       className="absolute inset-0 h-full w-full p-2"