site: topics axis + per-source indexes

Topics — the curated subscription layer: 18-value controlled vocabulary
in src/lib/topics.ts, enum-enforced by the content schema on finds and
reviews so unattended runs can't drift it. /topics/ index +
/topics/<t>/ pages with finds first-class alongside reviews, per-topic
RSS feeds that include finds (unlike category/tag feeds), "By topic"
section on /feeds/, Topics footer link and llms.txt section, dev-shim
coverage for the new feed URLs. daily-finds and build-review skills now
classify at capture/graduation time; "giftable" is a tag, never a
topic.

Per-source indexes: /sources/<slug>/ lists every review and find from a
source (catalog ∪ names in content, so retired sources resolve);
find/review colophons link "(more from this source)"; /sources/ cards
link "everything from this source →"; sub-3-item pages noindexed.

Claude-Session: https://claude.ai/code/session_01WZaczDJjL3xZ3u5spsN5AL

src/pages/sources.astro

@@ -135,6 +135,9 @@ const breadcrumbs = buildBreadcrumbs([
                       </li>
                     ))}
                   </ul>
+                  <p class="all-link">
+                    <a href={`/sources/${sourceSlug(source.name)}/`}>everything from this source →</a>
+                  </p>
                 </div>
               )}
             </div>
@@ -237,6 +240,10 @@ const breadcrumbs = buildBreadcrumbs([
       color: var(--muted);
     }
 
+    .all-link {
+      margin: 0.5rem 0 0;
+      font-size: 0.78rem;
+    }
     .recent {
       margin-top: 0.7rem;
       padding-top: 0.6rem;