refactor(migration): remove obsolete mirror extraction tooling

- delete extraction scripts that depended on the removed local mirror
- remove stale extract npm scripts and migration-brief references
- drop the old mirror ignore rule from .gitignore
- update reports and redirect reasons to use live-source wording

www/package.json

@@ -10,8 +10,6 @@
     "build": "astro build",
     "build:sandbox": "NODE_OPTIONS=--require=./tools/localhost-dns.cjs astro build",
     "preview": "astro preview",
-    "extract": "node tools/extract-fallback.mjs",
-    "extract:full": "node tools/extract-site.mjs",
     "extract:blog-footers": "node tools/extract-blog-footers.mjs",
     "crawl:live": "node tools/crawl-live-site.mjs",
     "audit:links": "node tools/audit-links.mjs",