fix: repair Renovate config, convert Makefile to go run, update GitHub Actions (#120)

* fix: repair Renovate config and convert Makefile to go run (#117)

- Remove non-existent `github>renovatebot/presets:golang` preset that
  broke Renovate PR creation
- Replace deprecated `fileMatch` with `managerFilePatterns` in
  customManagers
- Rewrite regex to match new Makefile pattern (renovate comment above
  version variable assignment)
- Fix `matchFileNames` glob pattern (`*.mk` -> `**/*.mk`)
- Convert all tool invocations from `go install` + global binary to
  `go run tool@version` for reproducible builds
- Convert npm global tools to `npx --yes` invocations
- Remove `dev-deps` and `check-deps` targets (tools auto-download)
- Add mdformat pre-commit hook with GFM support and config
- Add `fmt-md` Makefile target for manual markdown formatting
- Update local golangci-lint pre-commit hook to use `go run`
- Apply golangci-lint v2.10.1 auto-fixes (fmt.Fprintf optimization)
- Add nolint:gosec annotations for legitimate exec.Command usage
- Exclude .serena/ from mdformat and megalinter
- Add markdown indent_size=unset in .editorconfig for CommonMark compat

* chore(deps): update GitHub Actions to latest versions

- anthropics/claude-code-action: v1.0.34 -> v1.0.64
- actions/setup-go: v6.2.0 -> v6.3.0
- actions/upload-artifact: v6.0.0 -> v7.0.0
- goreleaser/goreleaser-action: v6.4.0 -> v7.0.0
- docker/login-action: v3.6.0 -> v3.7.0
- ivuorinen/actions: v2026.01.21 -> v2026.02.24

* fix: address code review feedback

- Fix issue template YAML frontmatter (replace underscore separators
  with proper --- delimiters); exclude templates from mdformat
- Replace string(rune(n)) with strconv.Itoa(n) in test files to produce
  deterministic numeric directory names instead of Unicode characters
- Remove stale `make dev-deps` reference in README, replace with
  `make dev-setup`
- Extract ban/unban format strings into shared.MetricsFmtBanOperations
  and shared.MetricsFmtUnbanOperations constants
- Replace hardcoded coverage percentages in README with evergreen
  phrasing

* fix: address round 2 code review feedback for PR #120

- Fix corrupted path traversal example in docs/security.md
- Fix Renovate .mk regex to match nested paths (.*\.mk$)
- Update checkmake pre-commit hook to v0.3.2 to match Makefile
- Add sync.WaitGroup to unsynchronized goroutines in security tests
- Fix fmt-md target to use pre-commit run mdformat
- Pin markdownlint-cli2 to v0.21.0 in lint-md target
- Standardize //nolint:gosec to // #nosec annotations for gosec CLI

* fix(ci): install PyYAML dependency for PR lint workflow

The pr-lint workflow uses ivuorinen/actions/pr-lint which internally
calls validate-inputs running a Python script that imports yaml.
Python was set up but PyYAML was never installed, causing
ModuleNotFoundError at runtime.

* fix: address round 3 code review feedback for PR #120

- Wrap Windows-style path traversal example in backtick code span so
  backslashes render literally in docs/security.md
- Add Renovate-managed MARKDOWNLINT_CLI2_VERSION variable in Makefile
  to match the pattern used by all other tool versions

CONTRIBUTING.md

@@ -3,7 +3,7 @@
 Thank you for your interest in contributing to **f2b**! Your help is appreciated,
 whether you are fixing bugs, adding features, improving documentation, or helping others.
 
----
+______________________________________________________________________
 
 ## How to Contribute
 
@@ -48,7 +48,7 @@ go test ./...
 - Describe your changes, reference related issues, and explain any design decisions.
 - Be ready to discuss and revise your code based on feedback.
 
----
+______________________________________________________________________
 
 ## Code Style
 
@@ -61,7 +61,7 @@ go test ./...
 - Handle sudo privileges securely - validate before escalation, use mocks in tests.
 - Use argument arrays for command execution, never shell string concatenation.
 
----
+______________________________________________________________________
 
 ## Security & Testing Guidelines
 
@@ -78,7 +78,7 @@ For comprehensive security guidelines, testing patterns, and examples, see:
 - [docs/testing.md](docs/testing.md) - Testing strategies and mock patterns
 - [AGENTS.md](AGENTS.md) - AI/LLM contributor guidelines
 
----
+______________________________________________________________________
 
 ## Communication
 
@@ -86,7 +86,7 @@ For comprehensive security guidelines, testing patterns, and examples, see:
 - Review the [Code of Conduct](CODE_OF_CONDUCT.md).
 - For large or breaking changes, open an issue to discuss your approach before submitting a PR.
 
----
+______________________________________________________________________
 
 ## Additional Notes
 
@@ -95,9 +95,10 @@ For comprehensive security guidelines, testing patterns, and examples, see:
 - If you are an AI/LLM agent, please see [AGENTS.md](AGENTS.md) for additional guidelines.
 - By contributing, you agree that your contributions will be licensed under the MIT License.
 
----
+______________________________________________________________________
 
 Thank you for helping make **f2b** better!
 
-[effective_go]: https://golang.org/doc/effective_go.html
 [contributing](CONTRIBUTING.md)
+
+[effective_go]: https://golang.org/doc/effective_go.html