Add web search knowledge base, message tagging, and word-memory tip topics

Introduces websearch.py (Tavily) + knowledge.py to ground chat responses
in search results, tagging.py to tag user and assistant messages via LLM
and pick related topics for the Discord useless-tips job, and
word_memory.py to track recent conversation nouns (surfaced in the new
WordPool.vue sidebar) used to pick tip topics close to a related tag.

frontend/src/components/MemoryMonitor.vue

@@ -74,7 +74,6 @@ onUnmounted(() => {
 .memory-monitor {
   background: #1a1a1a;
   border-top: 1px solid #333;
-  border-bottom: 1px solid #333;
   padding: 12px;
   font-size: 11px;
   font-family: monospace;