ci: DX glue + config/docs lint (.editorconfig, pre-commit, yamllint, markdownlint, lychee)

[VijitSingh97]

Closes #118. Finishes the tooling epic #116 (companion to #117, already merged).

Rounds out the non-shell tooling around RigForge's existing shellcheck/shfmt + kcov core. Mirrors the repo's conventions throughout: Makefile = single source of truth, pinned tool versions, and local == CI.

What's added

.editorconfig

Encodes the whitespace house style (shfmt -i 4, LF, insert_final_newline, and trim_trailing_whitespace — off for *.md so two-space line breaks survive) so editors match CI without per-editor setup.

pre-commit (extends the #117 seed)

.pre-commit-config.yaml now runs, on every commit:

• make lint (shellcheck + shfmt) as a local hook — reuses the Makefile's SHELL_FILES so there's no duplicated file list.
• gitleaks (kept from tooling: supply-chain & secrets hardening (gitleaks, Dependabot, zizmor) #117, same pinned version).
• freebies from pre-commit-hooks: detect-private-key, check-added-large-files, end-of-file-fixer, trailing-whitespace (with --markdown-linebreak-ext=md).

yamllint + markdownlint — new CI gates

• New Lint (yamllint) and Lint (markdownlint) jobs in ci.yml, plus make lint-yaml / make lint-md for local runs.
• Tuned configs (.yamllint, .markdownlint-cli2.yaml) that respect the repo's deliberate style (long explanatory lines, *asterisk* emphasis, Keep-a-Changelog duplicate headings, <details> HTML) while keeping the structural rules (blank lines around headings/lists/fences, code-fence languages, heading increments).
• Pinned via pipx (yamllint 1.38.0) and npx (markdownlint-cli2 0.22.1), same approach as the existing diff-cover/zizmor installs.

lychee — scheduled link check

• New links.yml workflow + make lint-links. Kept off the PR path (external links are flaky-by-nature, per the issue) — runs weekly + on demand. Pinned + checksum-verified binary, like the gitleaks/shellcheck installs.

Docs

Small fixes so the structural markdown rules pass: blank lines around headings/lists/fences (via markdownlint --fix), code-fence languages in the bug-report template, the README donation address as a fenced block, and the README hero subtitle as <h3> (keeps the look, clears the #→### heading jump).

Acceptance (#118)

• .editorconfig committed
• pre-commit runs shellcheck/shfmt/gitleaks + freebies locally; CONTRIBUTING.md updated
• yamllint + markdownlint green in CI; lychee green (scheduled)

Validation (ran locally)

• yamllint 1.38.0 --strict — clean across all 8 YAML files
• markdownlint-cli2 0.22.1 — 0 errors across 18 docs
• lychee 0.24.2 — 198 links, 0 errors
• zizmor (online) — no findings, incl. the new links.yml + ci.yml jobs
• pre-commit run --all-files — all six hooks pass; the freebie fixers made no changes (repo already clean)

Note

The two new PR gates (Lint (yamllint), Lint (markdownlint)) should be added to develop's required status checks — I'll do that once they report green here.

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