feat(config-audit): add 'mcp' kind to estimateTokens (v5 F2)

Differentiate MCP servers from generic 'item' (flat 15) — they actually
cost 500+ tokens per turn for protocol metadata and tool schemas.

estimateTokens(bytes, 'mcp', {toolCount}) returns max of:
- 500 token floor (base overhead)
- ceil(bytes / 3.5) (json-rate when bytes known)
- 500 + toolCount * 200 (when tool count is detected; Step 14 wires this)

Caller-side migration in next commit (Step 5).

Tests: +4 cases for mcp kind.

plugins/config-audit/scanners/lib/active-config-reader.mjs

@@ -22,12 +22,27 @@ const SCHEMA_VERSION = '1.0.0';
  * Estimate tokens for a given byte count and content kind.
  * Deterministic heuristic — see feature plan §4 for rationale.
  *
+ * MCP (v5 F2): an active MCP server consumes a base overhead of ~500 tokens
+ * for protocol metadata + tool schemas, even before any tool is described.
+ * When tool count is known (Step 14 wires this up), we estimate ~200 tokens
+ * per tool description.
+ *
  * @param {number} bytes - Byte count (or item count for kind='item')
- * @param {'markdown'|'frontmatter'|'json'|'item'} kind
+ * @param {'markdown'|'frontmatter'|'json'|'item'|'mcp'} kind
+ * @param {{toolCount?: number}} [opts] - kind-specific options (mcp: toolCount)
  * @returns {number} Integer token count (rounded up)
  */
-export function estimateTokens(bytes, kind = 'markdown') {
+export function estimateTokens(bytes, kind = 'markdown', opts = {}) {
   if (kind === 'item') return 15;
+  if (kind === 'mcp') {
+    const base = 500;
+    const perTool = 200;
+    const toolCount = typeof opts.toolCount === 'number' && opts.toolCount > 0 ? opts.toolCount : 0;
+    const safeBytes = typeof bytes === 'number' && bytes > 0 && Number.isFinite(bytes) ? bytes : 0;
+    const fromBytes = Math.ceil(safeBytes / 3.5);
+    const fromTools = base + toolCount * perTool;
+    return Math.max(base, fromBytes, fromTools);
+  }
   if (typeof bytes !== 'number' || bytes < 0 || !Number.isFinite(bytes)) return 0;
   if (kind === 'frontmatter') {
     const capped = Math.min(bytes, 600);