refactor: remove unused MCP server, CPM functions, and TaskProfile

Remove over-engineered subsystems with 0% production usage:
- MCP server (mcp.rs, 396 lines) — no consumers existed
- critical_path_weighted() and cpm_priorities() from DAG — scheduling
  uses simple lexicographic ordering, not CPM
- TaskProfile module (task_profile.rs, 69 lines) — only used by CPM
- 2 MCP test fixtures and 6 CPM test functions

All 229 remaining tests pass. Review protocol retained (actively used
by codex cross-model and parse-findings commands).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: z23cc