feat: Fix grapheme splitting and add automatic UMAP calculation

Critical fixes for core functionality:

1. Fixed grapheme-aware text splitting (app/api/nodes/route.ts)
   - Changed character-based substring to grapheme-ratio calculation
   - Now properly handles emojis and multi-byte characters
   - Prevents posts from exceeding 300 grapheme Bluesky limit
   - Added comprehensive logging for debugging

2. Automatic UMAP coordinate calculation (app/api/nodes/route.ts)
   - Triggers /api/calculate-graph automatically after node creation
   - Only when user has 3+ nodes with embeddings (UMAP minimum)
   - Non-blocking background process
   - Eliminates need for manual "Calculate Graph" button
   - Galaxy visualization ready on first visit

3. Simplified galaxy route (app/api/galaxy/route.ts)
   - Removed auto-trigger logic (now handled on insertion)
   - Simply returns existing coordinates
   - More efficient, no redundant calculations

4. Added idempotency (app/api/calculate-graph/route.ts)
   - Safe to call multiple times
   - Returns early if all nodes already have coordinates
   - Better logging for debugging

Implementation plans documented in /plans directory.

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

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

todo.md

@@ -3,3 +3,9 @@
 Upcoming items that should be implemented (time-permitting):
 
 - 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
+  general or on a specific node ID url there), it closes the modal automatically
+- 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