chore: update plugin catalog URL to git.fabledsword.com

Default plugins.index_url and all documentation URLs now point to
https://git.fabledsword.com/bvandeusen/FabledScryer-plugins.
Anchor /plugins/ in .gitignore so it only matches the root directory
(not docs/plugins/).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fabledscryer/core/settings.py

@@ -50,7 +50,7 @@ DEFAULTS: dict[str, Any] = {
     "ansible.sources": [],
     "ping.threshold.good_ms": 50,
     "ping.threshold.warn_ms": 200,
-    "plugins.index_url": "https://raw.githubusercontent.com/bvandeusen/fabledscryer-plugins/main/index.yaml",
+    "plugins.index_url": "https://git.fabledsword.com/bvandeusen/FabledScryer-plugins/raw/branch/main/index.yaml",
 }