feat: add built-in file editor with syntax highlighting

- Add CodeMirror 6 editor with support for 40+ languages
- Add file browser sidebar with directory tree navigation
- Add multi-tab support with dirty state indicators
- Add keyboard shortcuts (Ctrl+E, Ctrl+B, Ctrl+S, Ctrl+W)
- Add editor toggle button to status bar
- Editor uses current session's CWD and requires connection
- Add Tauri commands for file operations (list, read, write)

package.json

@@ -27,6 +27,31 @@
   },
   "license": "MIT",
   "dependencies": {
+    "@codemirror/lang-angular": "^0.1.4",
+    "@codemirror/lang-cpp": "^6.0.3",
+    "@codemirror/lang-css": "^6.3.1",
+    "@codemirror/lang-go": "^6.0.1",
+    "@codemirror/lang-html": "^6.4.11",
+    "@codemirror/lang-java": "^6.0.2",
+    "@codemirror/lang-javascript": "^6.2.4",
+    "@codemirror/lang-json": "^6.0.2",
+    "@codemirror/lang-less": "^6.0.2",
+    "@codemirror/lang-markdown": "^6.5.0",
+    "@codemirror/lang-php": "^6.0.2",
+    "@codemirror/lang-python": "^6.2.1",
+    "@codemirror/lang-rust": "^6.0.2",
+    "@codemirror/lang-sass": "^6.0.2",
+    "@codemirror/lang-sql": "^6.10.0",
+    "@codemirror/lang-vue": "^0.1.3",
+    "@codemirror/lang-wast": "^6.0.2",
+    "@codemirror/lang-xml": "^6.1.0",
+    "@codemirror/lang-yaml": "^6.1.2",
+    "@codemirror/language": "^6.12.1",
+    "@codemirror/legacy-modes": "^6.5.2",
+    "@codemirror/state": "^6.5.4",
+    "@codemirror/theme-one-dark": "^6.1.3",
+    "@codemirror/view": "^6.39.11",
+    "@lezer/highlight": "^1.2.3",
     "@tauri-apps/api": "^2",
     "@tauri-apps/plugin-clipboard-manager": "^2.3.2",
     "@tauri-apps/plugin-dialog": "^2",
@@ -36,6 +61,7 @@
     "@tauri-apps/plugin-os": "^2",
     "@tauri-apps/plugin-shell": "^2.3.4",
     "@tauri-apps/plugin-store": "^2",
+    "codemirror": "^6.0.2",
     "highlight.js": "^11.11.1",
     "marked": "^17.0.1"
   },