feat: migrate final Flickr image to local storage

Migrated the last remaining externally-hosted image:
- Downloaded cement-block.jpg from Flickr (farm3.static.flickr.com)
- Stored in content/images/2008-02-14/
- Updated classified-funny.md to use local path
- Converted markdown link to HTML to avoid MyST parser confusion

All external image dependencies (Flickr and WordPress) are now eliminated.
The blog is fully self-contained for images.

Author: offbyone

content/images/2008-02-14/cement-block.jpg

@@ -13,7 +13,7 @@ Apropos of nothing, here's a few funny Craigslist postings, culled from Metafilt
 
 [Hey, Crackhead](http://www.craigslist.org/about/best/sfo/27499971.html)
 
-[Cement Block, \$1](http://farm3.static.flickr.com/2416/2201688044_b9a72418e2_o.jpg)
+<a href="/images/2008-02-14/cement-block.jpg">Cement Block, $1</a>
 
 [Thank You Donkey Porn](http://www.craigslist.org/about/best/wdc/90359106.html)