Phase 1: PeerTube plugin and recon_domains module

Single source of truth for the 18 RECON knowledge domains mapped to
PeerTube category IDs 100-117. Replaces duplicate VALID_DOMAINS sets
in enricher.py and embedder.py with imports from lib/recon_domains.py.

Includes PeerTube plugin (peertube-plugin-recon-domains) that registers
custom categories via videoCategoryManager.addConstant(), and a parity
test to verify constants match between RECON and the PeerTube API.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

peertube-plugin/peertube-plugin-recon-domains/main.js

@@ -0,0 +1,28 @@
+async function register ({ videoCategoryManager }) {
+  const reconDomains = {
+    100: 'Agriculture & Livestock',
+    101: 'Civil Organization',
+    102: 'Communications',
+    103: 'Food Systems',
+    104: 'Foundational Skills',
+    105: 'Logistics',
+    106: 'Medical',
+    107: 'Navigation',
+    108: 'Operations',
+    109: 'Power Systems',
+    110: 'Preservation & Storage',
+    111: 'Security',
+    112: 'Shelter & Construction',
+    113: 'Technology',
+    114: 'Tools & Equipment',
+    115: 'Vehicles',
+    116: 'Water Systems',
+    117: 'Wilderness Skills'
+  }
+
+  for (const [id, label] of Object.entries(reconDomains)) {
+    videoCategoryManager.addConstant(parseInt(id), label)
+  }
+}
+
+module.exports = { register }