fix(lint): make the linter run again, and finish the em dash sweep

The linter had two faults stacked on top of each other.

First, the global `ajv: ^8.17.1` override starved @eslint/eslintrc, which
needs ajv 6 and passes it `missingRefs`; ajv 8 rejects that option, so ESLint
died before loading a single rule. Scoped overrides give eslint and
@eslint/eslintrc ajv 6.12.6 and leave the audit override in place everywhere
else.

Second, underneath that, `extends: ["@repo/config/eslint-preset.js"]` could
never resolve: ESLint's shareable-config naming convention rewrites it to
`@repo/eslint-config-config/...`. require.resolve hands ESLint a real path.

With the linter running it reported 35 react/no-unescaped-entities errors
across 7 files. Those are escaped rather than silenced, using ESLint's own
coordinates so only flagged text nodes were touched. Lint now exits 0. Two
@next/next/no-img-element warnings remain on the splash logos, which are
deliberate: theme-paired and fetchPriority="high".

Em dashes are also gone from the six blog posts and the README (105
occurrences), same rules as the site copy: colons for definition labels,
commas for appositives, semicolons for independent clauses.

package.json

@@ -31,6 +31,8 @@
       "minimatch": "^9.0.7",
       "picomatch": "^4.0.4",
       "ajv": "^8.17.1",
+      "eslint>ajv": "^6.12.6",
+      "@eslint/eslintrc>ajv": "^6.12.6",
       "brace-expansion": "^2.0.3",
       "postcss": "^8.5.14",
       "fast-uri": "^3.1.2"