v0.7.0 — signature registry, rl why, doctor --explain

v0.7.0 — max settings

The load-bearing heuristic gets armor, and the ledger learns to talk.

Added

• Test-runner signature registry — the pass/fail parser is now a per-toolchain registry covering jest/vitest, mocha/ava, pytest, go, cargo, tsc, eslint/ruff/mypy, gradle/maven, dotnet, playwright/cypress, and generic builds — backed by 18 real-output fixtures and a table-driven test. Adding YOUR runner is now the canonical first PR: one registry entry + one fixture + one table row.
• rl doctor --explain "<output>" — paste any test output, see exactly how it classifies (pass / fail / "ambiguous, left pending") and which pattern decided. No more guessing why the ledger marked something failed.
• rl why <file> — the roadmapped natural-language query, shipped: blocking failures with reasons, walls ("2 different attempts died on the same error — question the diagnosis"), retirements with receipts, passes.

Fixed

• Cargo/gradle failures caught by a generic counter now get their real error signature (panicked at..., BUILD FAILED) instead of a placeholder.

68 tests - benchmark still 120/120 caught, 0/190 false blocks - zero dependencies.