Initial implementation of compaction MCP server

Ephemeral, per-session context management for LLMs with 8 MCP tools:
store, query, status, compact, pin, forget, configure, update.

Features: scoring with decay/importance/access, Jaccard dedup,
summary promotion, budget-based eviction, auto-detection of
client context window via MCP hooks.

tokens.go

@@ -0,0 +1,10 @@
+package main
+
+// EstimateTokens returns a rough token count for a string.
+// Uses ~4 characters per token heuristic.
+func EstimateTokens(s string) int {
+	if len(s) == 0 {
+		return 0
+	}
+	return (len(s) + 3) / 4
+}