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-core/src/config.rs

@@ -54,11 +54,12 @@ impl GatewayConfig {
     /// Load configuration from a TOML file, with environment variable overrides.
     /// Env vars are prefixed with `CORTEX_` and use `__` as a separator
     /// (e.g. `CORTEX_GATEWAY__LISTEN=0.0.0.0:9000`).
-    pub fn load(path: impl AsRef<Path>) -> Result<Self, figment::Error> {
+    pub fn load(path: impl AsRef<Path>) -> Result<Self, Box<figment::Error>> {
         Figment::new()
             .merge(Toml::file(path))
             .merge(Env::prefixed("CORTEX_").split("__"))
             .extract()
+            .map_err(Box::new)
     }
 }