feat(electrobun): add xterm.js terminal with image addon (Sixel/iTerm2)

- Terminal.svelte component with @xterm/xterm + Canvas + Fit + Image addons
- Catppuccin Mocha terminal theme matching main app
- Sixel, iTerm2 inline image protocol support via xterm-addon-image
- ResizeObserver for responsive terminal sizing
- Demo cargo test output in terminal section below agent messages

ui-electrobun/package.json

@@ -11,6 +11,10 @@
 		"build:canary": "vite build && electrobun build --env=canary"
 	},
 	"dependencies": {
+		"@xterm/addon-canvas": "^0.7.0",
+		"@xterm/addon-fit": "^0.11.0",
+		"@xterm/addon-image": "^0.9.0",
+		"@xterm/xterm": "^6.0.0",
 		"electrobun": "latest"
 	},
 	"devDependencies": {