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).
