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.

skills/last30days/scripts/lib/ui.py

@@ -198,7 +198,7 @@ Just start with "last30" and talk to me like normal.
 
 # Shorter promo for single missing key
 PROMO_SINGLE_KEY = {
-    "reddit": "\n💡 Unlock TikTok and Instagram with SCRAPECREATORS_API_KEY - 10,000 free calls, no CC - scrapecreators.com\n",
+    "reddit": "\n💡 Unlock TikTok and Instagram with SCRAPECREATORS_API_KEY - 100 free credits, no CC - scrapecreators.com\n",
     "x": "\n💡 Unlock X: log into x.com in Firefox or Safari, then re-run. Or add AUTH_TOKEN/CT0 or XAI_API_KEY.\n",
     "web": "\n💡 You can unlock native grounded web search with BRAVE_API_KEY or SERPER_API_KEY.\n",
 }