feat(config-audit): TOK consumes readActiveConfig (v5 F1)

Removes the v4 'void readActiveConfig' placeholder and wires the
active-config snapshot into the TOK scanner.

Per-turn behavior changes:
- Each enabled MCP server becomes its own hotspot entry (richer than
  the parent .mcp.json file alone)
- total_estimated_tokens now includes MCP server cost
- result.activeConfig exposes a small summary
  (claudeMdEstimatedTokens, mcpServerCount, pluginCount, skillCount)

Failures of readActiveConfig are non-fatal — the scanner falls back
to the discovery-only path used in v4.

Tests: +3 cases on the new tok-active-config fixture
(.mcp.json with 2 servers, CLAUDE.md, plugin skeleton).

plugins/config-audit/tests/fixtures/tok-active-config/commands/sample.md

@@ -0,0 +1,11 @@
+---
+name: sample
+description: Sample command in the tok-active-config fixture
+model: sonnet
+---
+
+# /sample
+
+A trivial command body so the file has both frontmatter and content. The TOK
+scanner ranks command sources by their estimated tokens; this is bigger than
+zero, smaller than CLAUDE.md.