feat(lint): Add markdownlint integration

[currantw]

Summary

Integrate markdownlint-cli2 into the project's lint and format pipelines to enforce consistent markdown style across all .md files. This adds automated structural validation and auto-fix capability for markdown, complementing the existing C#, Rust, YAML, and GitHub Actions linting.

Issue Link

Closes #380.

Features and Behaviour Changes

• task lint:markdown — checks all markdown files for style violations.
• task format:markdown — auto-fixes markdown violations in-place.
• Both are wired into task lint and task format respectively.
• Uses npx markdownlint-cli2 (no separate install step needed, matches existing prettier pattern).
• Respects .gitignore via gitignore: true config option.

Implementation

• gitignore: true — automatically excludes gitignored directories (.kiro/, rust/target/, etc.).
• MD013 (line length) disabled — not auto-fixable, too noisy for prose-heavy docs.
• MD024 (duplicate headings) set to siblings_only — allows repeated headings under different parents.
• Explicit ignore for valkey-glide/** (read-only submodule containing .md files).

Limitations

⚪ None.

Testing

• task lint:markdown passes with 0 errors across 10 linted files
• task format:markdown runs successfully

Related Issues

⚪ None.

Checklist

• This Pull Request is related to one issue.
• Commit message has a detailed description of what changed and why.
• Tests are added or updated and all checks pass. (No tests applicable — CI/config tooling only)
• CHANGELOG.md, README.md, DEVELOPER.md, and other documentation files are updated.
• Destination branch is correct - main or release
• Create merge commit if merging release branch into main, squash otherwise.

[Copilot]

Pull request overview

Integrates markdownlint-cli2 into the repo’s existing task-based lint/format workflow to enforce consistent Markdown style across documentation and meta files.

Changes:

• Add task lint:markdown and task format:markdown, and wire them into task lint / task format.
• Introduce .markdownlint-cli2.yaml with project-specific rule/config overrides and ignore globs.
• Apply Markdown cleanup across several docs/templates to satisfy lint rules (heading levels, table separator, code-fence info strings, spacing).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Taskfile.yml	Adds markdown lint/format tasks and includes them in aggregate lint/format pipelines.
.markdownlint-cli2.yaml	Configures markdownlint-cli2 (rule overrides, gitignore integration, submodule ignores).
docs/configuration-architecture-analysis.md	Markdown formatting updates (blank lines, fenced code language).
docs/ci-cd.md	Markdown table separator formatting update.
DEVELOPER.md	Heading level and lint/format command list updates to include markdown tasks.
AGENTS.md	Updates “common commands / quality gates” to include markdown lint/format tasks.
.github/pull_request_template.md	Normalizes headings/structure to comply with Markdown linting.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.