docs(plans): update docstring pricing to $14 / $29

Updates the plans.py module docstring to reflect the new pricing:
  - Pro: $19 → $14
  - Business: $49 → $29

The docstring is the only place in the codebase that hard-codes prices.
The user-facing PricingPage renders via Clerk's <PricingTable /> component,
which pulls live prices from the Clerk Dashboard configuration — so the
numbers visitors see will change the moment Clerk is updated, not with
this commit.

Kept the "business" slug so existing subscriptions and code references
keep working. A follow-up will rename the display name to "Pro Plus"
once the Clerk product is renamed in the dashboard (same slug, new
display name).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Sbussiso

backend/app/core/plans.py

@@ -3,8 +3,9 @@
 
 Plan slugs must match the keys defined in the Clerk Dashboard:
   - free_org  (Free)
-  - pro       (Pro — $19/mo)
-  - business  (Business — $49/mo)
+  - pro       (Pro — $14/mo)
+  - business  (Business — $29/mo; will be renamed "Pro Plus" once the
+               Clerk product is renamed in the dashboard)
 """
 
 import logging