docs: remove GitHub, gitea.redbearos.org is the only git server

Remove origin remote (GitHub). Rename gitea to origin. Update all
AGENTS.md references to remove GitHub mentions.

AGENTS.md

@@ -51,7 +51,7 @@ Any of the following that runs without the user explicitly requesting it:
 - `git clone`, `git fetch`, `git pull` against any remote
 - `wget` or `curl` downloading source code or build artifacts
 - Any HTTP request to `gitlab.redox-os.org`, `github.com`, `static.redox-os.org`, or any other
-  upstream hosting service
+  upstream hosting service (note: Red Bear OS does not use GitHub — see Repository Hosting below)
 
 ### What Does NOT Count
 
@@ -191,7 +191,8 @@ make all
 - **Build templates**: `cargo`, `meson`, `cmake`, `make`, `configure`, `custom`
 - **WIP recipes**: Must start with `#TODO` comment explaining what's missing
 - **Custom configs**: Name with `my-` prefix (git-ignored by convention)
-- **CI**: GitLab CI (`.gitlab-ci.yml`) at root + per-recipe; some have GitHub Actions
+- **CI**: GitLab CI (`.gitlab-ci.yml`) at root + per-recipe
+- **Repository Hosting**: Gitea at `gitea.redbearos.org` — the ONLY git server. No GitHub.
 - **Syscall ABI**: Unstable intentionally. Stability via `libredox` and `relibc`
 - **Drivers**: ALL userspace daemons via scheme system. No kernel-space drivers (except serio)
 
@@ -380,9 +381,8 @@ When reordering patches: remove the source tree, re-fetch, and rebuild to verify
 
 ### Large Patch Files (redox.patch)
 
-`local/patches/base/redox.patch` (consolidated mega-patch) exceeds GitHub's
-100 MB file size limit. It is stored as 90 MB chunks under
-`local/patches/base/redox-patch-chunks/` and reassembled by:
+`local/patches/base/redox.patch` (consolidated mega-patch) is stored as 90 MB
+chunks under `local/patches/base/redox-patch-chunks/` and reassembled by:
 ```bash
 local/patches/base/reassemble-redox-patch.sh
 ```

recipes/AGENTS.md

@@ -45,8 +45,8 @@ cat > recipes/<category>/<name>/recipe.toml << 'EOF'
 #TODO: describe what's missing (required for WIP)
 
 [source]
-git = "https://github.com/user/repo.git"
-upstream = "https://github.com/original/repo.git"
+git = "https://gitea.redbearos.org/user/repo.git"
+upstream = "https://gitea.redbearos.org/original/repo.git"
 branch = "redox"
 
 [build]