fix: browser_tests Phase 1 - mechanical fixes

- Rename dragAndDrop to dragDrop (7 occurrences)

- Add override modifiers in SidebarTab.ts (4 fixes)

- Remove .ts import extensions in actionbar.spec.ts

- Prefix unused variables with underscore (9 files)

- Fix ESLint import() type annotation in globals.d.ts

Reduces typecheck:browser errors from 229 to 215

Amp-Thread-ID: https://ampcode.com/threads/T-019c1787-c781-761d-b95a-4844e909e64c
Co-authored-by: Amp <amp@ampcode.com>

docs/guidance/playwright.md

@@ -14,6 +14,21 @@ See `docs/testing/*.md` for detailed patterns.
 - Prefer specific selectors (role, label, test-id)
 - Test across viewports
 
+## Window Globals
+
+Browser tests access `window.app`, `window.graph`, and `window.LiteGraph` which are
+optional in the main app types. In E2E tests, use non-null assertions (`!`):
+
+```typescript
+window.app!.graph!.nodes
+window.LiteGraph!.registered_node_types
+```
+
+This is the **only context** where non-null assertions are acceptable.
+
+**TODO:** Consolidate these references into a central utility (e.g., `getApp()`) that
+performs proper runtime type checking, removing the need for scattered `!` assertions.
+
 ## Test Tags
 
 Tags are respected by config: