tooling: formatting baseline (.editorconfig + Prettier + markdownlint)

[VijitSingh97]

Part of the v1.1 site-tooling set · companion to #11.

No formatting/lint baseline for contributions — whitespace and YAML/HTML/Markdown style are unenforced.

Proposal

• .editorconfig (charset, indent, final newline, trim trailing whitespace).
• Prettier over HTML/CSS/JS/YAML/MD (with a .prettierignore for generated/vendored files).
• markdownlint for any Markdown content.
• Wire as a CI lint job and (optionally) a pre-commit hook, mirroring the siblings' pre-commit approach.

Acceptance

• .editorconfig present.
• Prettier + markdownlint run in CI (check mode).
• Repo reformatted once to a clean baseline.