docs: add .github repo to ecosystem documentation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: baijum

docs/ecosystem.md

@@ -6,7 +6,8 @@ The Towlion GitHub organization serves as a catalog of deployable applications.
 
 ```
 towlion/
-  platform            # Architecture docs and platform tools (github.com/towlion/platform)
+  .github              # Organization profile and community health files
+  platform             # Architecture docs and platform tools (github.com/towlion/platform)
   app-template         # Template for bootstrapping new apps (github.com/towlion/app-template)
   uku-companion        # Music practice companion
   fretboard-trainer    # Guitar fretboard learning tool
@@ -16,6 +17,12 @@ towlion/
 
 ## Repository Types
 
+### Organization Profile ([`towlion/.github`](https://github.com/towlion/.github))
+
+The special `.github` repository provides the organization-level profile README displayed on [github.com/towlion](https://github.com/towlion). Contains:
+
+- `profile/README.md` — marketing content shown on the org landing page
+
 ### Platform Repository (`towlion/platform`)
 
 The meta repository for the ecosystem. Contains: