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>

Cargo.toml

@@ -10,7 +10,7 @@ members = [
 [workspace.package]
 version = "0.1.0"
 edition = "2024"
-license = "GPL-3.0"
+license = "GPL-3.0-or-later"
 repository = "https://git.lair.cafe/helexa/cortex"
 
 [workspace.dependencies]