Add CI log privacy guide (#35)

[Photon101]

Summary

Adds a CI log privacy guide covering log sanitization, data that should never be pasted publicly, and good public evidence for Maven failures. The guide is linked from SECURITY.md, CONTRIBUTING.md, and the README document index.

Closes #35.

MVP Validation Checklist

• Relevant local checks were run, or this is a documentation-only/no-runtime-impact PR and the reason is explained below
• User-facing CLI, output, or JSON changes include focused CLI, smoke, golden, schema, or compatibility validation
• Parser, fixture, or report changes include sanitized fixtures and fixture integrity validation when applicable
• Documentation, examples, compatibility, and local-first impact are updated or called out when applicable

This is a documentation-only change. It does not change CLI behavior, parser behavior, fixtures, JSON output, provider behavior, telemetry, or external-service dependencies.

Validation

• go test ./...
• go vet ./...
• CLI behavior tested when user-facing output changes
• Golden files updated when text output intentionally changes
• Documentation updated when contributor or user behavior changes
• No GitHub, GitLab, AI provider, telemetry, or external-service dependency was added to core analysis
• JSON compatibility was preserved or the compatibility impact is explained
• Branch name, PR title, and commit messages avoid coding agent or tool names

Scope

• This PR is focused on one issue or one clearly bounded change
• No unrelated refactors
• No generated binaries, private logs, or local cache files committed
• Issue and PR labels match the type, area, stage, and status guidance when applicable

[github-actions]

Hi @Photon101, thank you for contributing to PR Maven CLI.

I appreciate the time you spent opening this pull request. This project is intentionally shaped for focused, reviewable open source contributions, so your input helps the tool become more useful for Java and Maven teams.

A maintainer will review the context, labels, and next steps as soon as possible. If this is your first contribution here, welcome aboard.

Useful links:

• Contributing guide: CONTRIBUTING.md
• Testing guide: docs/testing.md
• CI/CD guide: docs/ci.md

Thank you for helping build a deterministic, local-first Maven failure triage tool.