feat: story-driven mock data for demos + fix hydration error

Rewrote mock data generator with deterministic, story-driven characters
that demonstrate real insights: expensive model trap, long conversation
cost spikes, day-1 plan exhaustion, inactive seats, spend concentration,
and version-adoption correlation.

Fix hydration mismatch in dashboard time range picker caused by reading
localStorage during SSR initialization.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ofershap

.gitignore

@@ -12,3 +12,4 @@ coverage/
 .env.local
 .env.*.local
 .DS_Store
+tmp/