docs: correct ScrapeCreators free tier to 100 credits (closes #367)

The skill advertises ScrapeCreators as offering "10,000 free API calls" in
six places. The actual free tier on the ScrapeCreators pricing page is
"100 credits free · No credit card required · Credits never expire" — a
100x overstatement that surprises users on signup.

Reporter (#367) burned through their full free allocation on a single
/last30days run after taking the 10,000-call claim at face value. They
verified the actual tier directly against scrapecreators.com plus an
independent review at fahimai.com.

Sweep:
- hooks/scripts/check-config.sh:110  (SessionStart hook tip line)
- README.md:228                      (Sources × Cost table row)
- HERMES_SETUP.md:62                 (Optional: ScrapeCreators bullet)
- skills/last30days/scripts/lib/ui.py:199  (PROMO_SINGLE_KEY["reddit"])
- skills/last30days/SKILL.md:1648    ("PAYG after 10,000 free API calls")
- skills/last30days/SKILL.md:1661    ("10,000 free API calls, then PAYG")

Wording defaults to the provider's own framing — "100 free credits" — and
keeps PAYG language where it was already explicit, since the paid step is
the part users were actually getting blindsided by.

CI gates: tests/test_plugin_contract.py (4) + tests/test_version_consistency.py (4)
all pass.  shellcheck clean.  No tests pin the "10,000" string.

hooks/scripts/check-config.sh

@@ -120,6 +120,6 @@ else
   # Setup done but missing ScrapeCreators — recommend it
   echo "/last30days: Ready — ${SOURCE_COUNT} sources active."
   echo "  Tip: Add ScrapeCreators for Reddit comments + TikTok + Instagram."
-  echo "  10,000 free API calls, no credit card — scrapecreators.com"
+  echo "  100 free credits, no credit card — scrapecreators.com"
   echo "  last30days has no affiliation with any API provider."
 fi