fix: address PR #93 review issues

- Remove translate-x/translate-y CSS selectors that broke layout utilities
  (AssistantPanel slide animation, DebugLogViewer resize handle)
- Add browser validation to get_playwright_browser() with warning for
  invalid values (matches get_playwright_headless() behavior)
- Remove phantom SQLite documentation from CUSTOM_UPDATES.md that
  described features not present in PR #93
- Update checklist and revert instructions to match actual changes

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

client.py

@@ -59,6 +59,10 @@ def get_playwright_headless() -> bool:
     return value in truthy
 
 
+# Valid browsers supported by Playwright MCP
+VALID_PLAYWRIGHT_BROWSERS = {"chrome", "firefox", "webkit", "msedge"}
+
+
 def get_playwright_browser() -> str:
     """
     Get the browser to use for Playwright.
@@ -67,7 +71,13 @@ def get_playwright_browser() -> str:
     Options: chrome, firefox, webkit, msedge
     Firefox is recommended for lower CPU usage.
     """
-    return os.getenv("PLAYWRIGHT_BROWSER", DEFAULT_PLAYWRIGHT_BROWSER).lower()
+    value = os.getenv("PLAYWRIGHT_BROWSER", DEFAULT_PLAYWRIGHT_BROWSER).strip().lower()
+    if value not in VALID_PLAYWRIGHT_BROWSERS:
+        print(f"   - Warning: Invalid PLAYWRIGHT_BROWSER='{value}', "
+              f"valid options: {', '.join(sorted(VALID_PLAYWRIGHT_BROWSERS))}. "
+              f"Defaulting to {DEFAULT_PLAYWRIGHT_BROWSER}")
+        return DEFAULT_PLAYWRIGHT_BROWSER
+    return value
 
 
 # Feature MCP tools for feature/test management