v0.6: Add benchmark lifecycle and mutation/exploit gates

[t3chn]

Closes #18.

Summary:

• Adds task-family lifecycle statuses and lifecycle metadata for all current task families.
• Adds hardening gate metadata for decision-grade families, including mutation smoke declarations and exploit smoke status.
• Adds lifecycle, mutation-smoke, and hardening-check scripts with Make targets and CI wiring.
• Adds benchmark lifecycle docs, mutation/exploit gate docs, suite strategy docs, and report schema v1 guidance.
• Adds tests for lifecycle config, hardening config, and mutation smoke output.

Non-goals:

• no new task family;
• no browser workflow;
• no live MCP;
• no private bundle runtime;
• no consumer app integration;
• no real customer data;
• no private holdouts in public repo.

Test plan:

• make validate
• make test
• make smoke
• make compare-smoke
• make if01-smoke
• make data01-smoke
• make doc01-smoke
• make sup01-smoke
• make api01-smoke
• make lifecycle-check
• make mutation-smoke
• make hardening-check
• make leak-check
• python3 -m ruff check .
• git diff --check