perf(tui): optimize image line detection and box cache (#1084)

- Add isImageLine() to terminal-image.ts with single startsWith check based on detected terminal protocol
- Replace dual includes() checks in tui.ts with imported isImageLine()
- Add image line handling to markdown.ts to skip wrapping and margins for image escapes
- Consolidate Box cache into RenderCache type with childLines/width/bgSample/lines fields
- Use in-place mutation in applyLineResets() to avoid array allocation

package-lock.json

@@ -6084,6 +6084,15 @@
 			],
 			"license": "BSD-3-Clause"
 		},
+		"node_modules/ignore": {
+			"version": "7.0.5",
+			"resolved": "https://registry.npmjs.org/ignore/-/ignore-7.0.5.tgz",
+			"integrity": "sha512-Hs59xBNfUIunMFgWAbGX5cq6893IbWg4KnrjbYwX3tx0ztorVgTDA6B2sxf8ejHJ4wz8BqGUMYlnzNBer5NvGg==",
+			"license": "MIT",
+			"engines": {
+				"node": ">= 4"
+			}
+		},
 		"node_modules/immediate": {
 			"version": "3.0.6",
 			"resolved": "https://registry.npmjs.org/immediate/-/immediate-3.0.6.tgz",
@@ -9051,6 +9060,7 @@
 				"diff": "^8.0.2",
 				"file-type": "^21.1.1",
 				"glob": "^11.0.3",
+				"ignore": "^7.0.5",
 				"marked": "^15.0.12",
 				"minimatch": "^10.1.1",
 				"proper-lockfile": "^4.1.2",