NFR 11: Continuous Integration (GitHub Actions)

[itsniper]

Goal

Add CI (GitHub Actions) to the project so that every push / PR runs the build, tests, lint, and docs generation. Currently there is no automated verification.

Context

See the investigation report at docs/investigations/swift6-concurrency-audit-2026-05-13.md, Preventive Measures section. The audit recommends several "shift-left" guardrails that only pay off when wired into CI:

• swift build + swift test under -strict-concurrency=complete
• SwiftLint custom rules banning @unchecked Sendable and @preconcurrency import outside Sources/ReliaBLEMock/
• DocC build (swift package generate-documentation) so public-API renames break the docs build, not silent drift
• (Future) test coverage reporting

Deliverable

1. .github/workflows/ci.yml triggered on PRs and pushes to main:
   • Run swift build and swift test on macOS-15 (or latest, matching iOS 18+ / macOS 15+ targets).
   • Run SwiftLint with custom rules from the investigation report's Preventive Measures section.
   • Run swift package generate-documentation (see sub-issue) and fail on warnings.
2. SwiftLint config (.swiftlint.yml) with the custom rules:

   custom_rules:
     no_unchecked_sendable:
       name: "@unchecked Sendable banned"
       regex: '@unchecked\s+Sendable'
       included: "Sources/ReliaBLE/.*\\.swift"
       severity: error
     no_preconcurrency_import:
       name: "@preconcurrency import banned"
       regex: '@preconcurrency\s+import'
       included: "Sources/ReliaBLE/.*\\.swift"
       severity: error

3. Branch protection (manual step, document in this issue): require CI to pass on PRs to main.

Sub-issues

• DocC build in CI (separate sub-issue tracked below).

Acceptance criteria

• A green CI badge appears in README.md.
• Opening a PR triggers all three checks (build/test, lint, docs) and they pass on the current main.
• Branch protection enforces passing CI before merge to main.

References

• Investigation report: docs/investigations/swift6-concurrency-audit-2026-05-13.md (Preventive Measures)
• Related NFR: NFR 2: Automated Testing #9 (Automated Testing) — this issue is the CI scaffolding that makes NFR 2: Automated Testing #9 enforceable.