refactor: detect md hard-wraps via mdast AST, not regex

Per review feedback (use a real markdown parser with an AST linked to
source positions), rewrite verify-md-wrap to parse each file with
mdast-util-from-markdown (the CommonMark parser behind remark) + the GFM
extension, then flag any `paragraph` node whose source span covers more
than one line.

Why a parser over the hand-rolled line scanner:
- It is a checker, not a formatter — it reports and never rewrites, so
  zero cosmetic churn (no emphasis-marker or table-delimiter
  normalization, which is why Prettier was rejected for this).
- The AST owns every structural exemption (fenced code of any fence
  length, tables, lists, blockquotes, HTML, headings, reference defs),
  fixing both bugs the regex version had: it now catches wrapped
  list-item / blockquote prose (a `paragraph` inside those nodes) and no
  longer false-positives on a longer ```` fence wrapping an inner ```.

Also unwrap two pre-existing hard-wrapped blockquotes (architecture.md,
adding-a-tool.md) that the stricter AST check correctly surfaced.

package.json

@@ -35,12 +35,16 @@
   },
   "devDependencies": {
     "@stylistic/eslint-plugin": "^5.10.0",
+    "@types/mdast": "^4.0.4",
     "@types/node": "^25.3.5",
     "@vitest/coverage-v8": "^4.1.8",
     "eslint": "^10.4.1",
     "fast-check": "^4.8.0",
     "knip": "^6.16.1",
     "lefthook": "^2.1.9",
+    "mdast-util-from-markdown": "^2.0.3",
+    "mdast-util-gfm": "^3.1.0",
+    "micromark-extension-gfm": "^3.0.0",
     "publint": "^0.3.21",
     "tsdown": "^0.22.2",
     "tsx": "^4.22.4",