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>

lib/recon_domains.py

@@ -0,0 +1,34 @@
+"""
+RECON Domain Taxonomy
+
+Single source of truth for the 18 knowledge domains and their PeerTube
+category ID mappings. IDs 100-117 are registered via the
+peertube-plugin-recon-domains plugin.
+
+Import VALID_DOMAINS from here instead of defining local sets.
+"""
+
+DOMAIN_CATEGORY_MAP = {
+    'Agriculture & Livestock': 100,
+    'Civil Organization': 101,
+    'Communications': 102,
+    'Food Systems': 103,
+    'Foundational Skills': 104,
+    'Logistics': 105,
+    'Medical': 106,
+    'Navigation': 107,
+    'Operations': 108,
+    'Power Systems': 109,
+    'Preservation & Storage': 110,
+    'Security': 111,
+    'Shelter & Construction': 112,
+    'Technology': 113,
+    'Tools & Equipment': 114,
+    'Vehicles': 115,
+    'Water Systems': 116,
+    'Wilderness Skills': 117,
+}
+
+VALID_DOMAINS = set(DOMAIN_CATEGORY_MAP.keys())
+
+CATEGORY_DOMAIN_MAP = {v: k for k, v in DOMAIN_CATEGORY_MAP.items()}