ci: add Gitea CI, RPM spec, license, and repo hygiene

- Add .gitea/workflows/ci.yml with fmt/clippy/test on all branches
  and SRPM build + COPR publish on version tags
- Add cortex.spec for Fedora RPM packaging
- Add GPL-3.0-or-later LICENSE file
- Add cortex.example.toml with generic hostnames; gitignore cortex.toml
- Scrub infrastructure-specific hostnames from README.md, CLAUDE.md,
  and doc comments
- Fix unused imports and clippy warnings to pass -D warnings
- Fix missing deps (bytes, reqwest, serde_json) exposed during build
- Run cargo fmt across workspace
- Update SPDX license identifier to GPL-3.0-or-later

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

crates/cortex-gateway/src/proxy.rs

@@ -39,8 +39,8 @@ pub async fn forward_request(
 
     let upstream_resp = req_builder.send().await.map_err(ProxyError::Upstream)?;
 
-    let status = StatusCode::from_u16(upstream_resp.status().as_u16())
-        .unwrap_or(StatusCode::BAD_GATEWAY);
+    let status =
+        StatusCode::from_u16(upstream_resp.status().as_u16()).unwrap_or(StatusCode::BAD_GATEWAY);
 
     let resp_headers = upstream_resp.headers().clone();
     let stream = upstream_resp.bytes_stream();