feat: Add Playwright testing scaffolding infrastructure

Implements complete Playwright testing infrastructure for manual MCP testing and
as foundation for Magnitude tests.

Created:
- playwright.config.ts - Main configuration with setup project
- tests/playwright/auth.setup.ts - Authentication setup (placeholder)
- tests/playwright/fixtures.ts - Custom fixtures for authenticated/page contexts
- tests/playwright/helpers/chat.ts - Chat interaction helpers
- tests/playwright/helpers/galaxy.ts - Galaxy visualization helpers
- tests/playwright/helpers/node.ts - Node creation/management helpers
- tests/playwright/smoke.spec.ts - Basic smoke tests
- .env.test - Environment variables template

Updated:
- package.json - Added test:playwright scripts
- .gitignore - Added tests/playwright/.auth/ exclusion

Ready for manual Playwright MCP testing and Magnitude test creation.

Resolves plan: 01-playwright-scaffolding.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

todo.md

@@ -2,6 +2,9 @@
 
 Upcoming items that should be implemented (time-permitting):
 
+- add base playwright scaffolding files to improve the efficiency of manual
+  playwright mcp testing as well as that of magnitude
+- ADD MAGNITUDE TESTS FOR EVERYTHING, both existing and new additions
 - stream the AI output to deepgram for faster synthesis
 - fix the freaking galaxy node clicking -- when going directly to a node ID
   link, it redirects to /chat; when clicking on a node in /galaxy (either
@@ -9,3 +12,5 @@ Upcoming items that should be implemented (time-permitting):
 - dark mode/light mode favicon and overall app theme
 - fix the double border on desktop between sidebar and conversation actions UI
 - delete "backup"/"old" page.tsx files
+- allow ai to transition to edit in chat
+- why wait for three nodes before umap?