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-cli/src/main.rs

@@ -42,9 +42,8 @@ async fn main() -> Result<()> {
 
     match cli.command {
         Commands::Serve { config } => {
-            let cfg = GatewayConfig::load(&config).map_err(|e| {
-                anyhow::anyhow!("failed to load config from '{config}': {e}")
-            })?;
+            let cfg = GatewayConfig::load(&config)
+                .map_err(|e| anyhow::anyhow!("failed to load config from '{config}': {e}"))?;
 
             tracing::info!(
                 nodes = cfg.nodes.len(),