chore: enforce minimal markdown table formatting

Prettier pads markdown table cells for column alignment, which turns any
content change into a table-wide realignment diff. Markdown was only in
prettierignore for packages/kilo-vscode/; the root formatter still
repadded docs elsewhere (e.g. TESTING.md, kilo-docs, AGENTS.md).

Adds *.md to the root .prettierignore, documents the convention in
AGENTS.md, and adds script/check-md-table-padding.ts + a workflow to
enforce it. Existing padded tables in Kilo-owned docs have been
rewritten via the script's --fix mode.

.github/pull_request_template.md

@@ -13,8 +13,8 @@ Some description of HOW you achieved it. Perhaps give a high level description o
 ## Screenshots
 
 | before | after |
-| ------ | ----- |
-|        |       |
+|---|---|
+|  |  |
 
 ## How to Test