Raise default rate limits for internal firm deployment

The original defaults (300 general / 30 chat / 60 chat-create / 50
upload per 15-minute window) were tuned tight enough that one
person debugging a flow could easily hit them and see the generic
"Too many requests" message in the browser with no obvious
correlation back to what triggered it.

Raise the defaults to numbers that suit normal multi-user firm
use without rebuilding when an operator wants to bump them
further:

  general     300  -> 1500   per IP, per 15 min
  chat         30  -> 200    per user, per 15 min
  chat-create  60  -> 300    per user, per 15 min
  upload       50  -> 300    per user, per hour

All four remain tunable via the same env var names so deployments
that want stricter limits (or stricter for a specific window) can
still set them. Documented in .env.compose.example.