Run prettier across the repo, exclude the lockfile from it

Prettier had never been run in --check mode here before, so this had
drifted across most files (markdown tables, long option() chains,
line wrapping). Purely formatting, no logic changes - needed so a CI
format:check gate can actually pass. Adds .prettierignore for
pnpm-lock.yaml specifically: prettier's YAML formatter rewrites every
quoted key (single -> double quotes) producing an ~8700-line diff of
pure noise on a file pnpm itself owns the formatting of.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/scripts/cleanup.js

@@ -10,7 +10,9 @@ const targetDir = getArg("--dir");
 const olderThanDays = getArg("--days");
 const types = getArg("--types");
 
-console.log(`Scanning ${targetDir} for files older than ${olderThanDays} days (types: ${types})`);
+console.log(
+  `Scanning ${targetDir} for files older than ${olderThanDays} days (types: ${types})`,
+);
 if (process.env.CLEANUP_API_KEY) {
   console.log("Using configured external API key.");
 }