feat(renderer): ImageViewerPane with zoom, pan, and metadata

[khang859]

Summary

• Adds ImageViewerPane component replacing the Mission 1 placeholder for paneType: 'image' panes
• Adds FILE_READ_BINARY IPC channel (constants + main handler + preload) to load image files as base64 blob URLs — works in both dev and production mode
• Supports PNG, JPG, JPEG, GIF, WebP, SVG, BMP, ICO

Features

• Default: Fit-to-window (image scaled to fill pane, re-fits on resize)
• Zoom: Scroll wheel, +/- keys, floating toolbar buttons
• Double-click: Toggle between fit-to-window and 100% actual size
• Pan: Click-drag when zoomed in; grab/grabbing cursor feedback
• Zoom indicator: Bottom-right overlay showing current percentage
• Reset: 0 key resets to fit-to-window
• Floating toolbar: Top-right, appears on hover — Zoom In, Zoom Out, Fit, 1:1 buttons
• Checkerboard background: Standard transparency indicator pattern
• Status bar: Filename, image dimensions (W × H), file size (human-readable)

Test plan

• Open a PNG — image shows fit-to-window, status bar shows filename/dimensions/size
• Scroll wheel zooms in/out smoothly, zoom % indicator updates
• Double-click toggles fit ↔ 100%
• Click-drag pans when zoomed in
• 0 resets to fit, +/- zoom in/out
• Floating toolbar appears on hover
• PNG with transparency shows checkerboard behind it
• Works with JPG, GIF, SVG, WebP
• npm run build passes ✅

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