Finish the move off weblorgmigrate-to-orgo

Remove what the migration left behind, then cut build.py down to the work
orgo does not do: 443 lines to 168.

- Delete publish.el and theme/templates/, superseded by content/orgo.toml
  and content/templates/. theme/static/ stays; orgo publishes it as assets.
- Drop the tag builder, the org-source copy, and the helpers that only fed
  them. orgo generates /tags/ and a page per tag from a collection.
- Rewrite the README and the migration-era comments that explained the
  config by pointing at what weblorg used to do.
- Serve styles.css as authored. Minifying 1KB of CSS saved 52 bytes over
  the wire once compressed, which did not pay for a build step and a
  toolchain dependency.
- Stop wiping the output directory. The .orgo-cache.json inside it is what
  makes a build incremental, and orgo already prunes outputs whose source
  is gone and re-emits any that are missing. Production keeps .build/ and
  development gets .build-dev/, because production rewrites image URLs in
  the output and a shared directory would let one environment reuse pages
  rendered for the other.

An incremental build is byte-identical to a clean one, and the site output
is unchanged apart from the /uses/ stack row.

1 files changed, 4 insertions, 5 deletions

diff --git a/content/templates/feed.xml b/content/templates/feed.xml
index fa761b8..7596b02 100644
--- a/content/templates/feed.xml
+++ b/content/templates/feed.xml
@@ -1,10 +1,9 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-{#- The RSS feed at /feed.xml, mirroring theme/templates/feed.xml. A feed is read away
-    from the site that served it, so every URL here is absolute — which is what
-    `| absolute` needs [site] base_url for.
+{#- The RSS feed at /feed.xml. A feed is read away from the site that served it, so
+    every URL here is absolute — which is what `| absolute` needs [site] base_url for.
 
-    <description> carries each post's full rendered HTML, as weblorg's feed does — the
-    collection sets `include_content` to ask for it. #}
+    <description> carries each post's full rendered HTML — the collection sets
+    `include_content` to ask for it. #}
 <rss version="2.0"
      xmlns:content="http://purl.org/rss/1.0/modules/content/"
      xmlns:dc="http://purl.org/dc/elements/1.1/"