chore: Fix all lint errors and remove unused code

- Fix 75 ESLint errors by updating eslint.config.mjs:
  - Add missing browser globals (MouseEvent, AbortController, Response, etc.)
  - Add Vite define global (__APP_VERSION__)
  - Configure @ts-nocheck to require descriptions
  - Add no-unused-vars rule for .mjs scripts

- Fix runtime bug in agent-output-modal.tsx (setOutput -> setStreamedContent)

- Remove ~120 unused variable warnings across 97 files:
  - Remove unused imports (React hooks, lucide icons, types)
  - Remove unused constants and variables
  - Remove unused function definitions
  - Prefix intentionally unused parameters with underscore

- Add descriptions to all @ts-nocheck comments (25 files)

- Clean up misc issues:
  - Remove invalid deprecation plugin comments
  - Fix eslint-disable comment placement
  - Add missing RefreshCw import in code-view.tsx

Reduces lint warnings from ~300 to 67 (all remaining are no-explicit-any)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/scripts/kill-test-servers.mjs

@@ -29,7 +29,7 @@ async function killProcessOnPort(port) {
           try {
             await execAsync(`kill -9 ${pid}`);
             console.log(`[KillTestServers] Killed process ${pid}`);
-          } catch (error) {
+          } catch (_error) {
             // Process might have already exited
           }
         }
@@ -47,7 +47,7 @@ async function killProcessOnPort(port) {
       await new Promise((resolve) => setTimeout(resolve, 500));
       return;
     }
-  } catch (error) {
+  } catch (_error) {
     // No process on port, which is fine
   }
 }