Add live-load routing tie-break and provider pin

[nestharus]

Summary

• Add DB-backed recent-running live-load counts per provider and use them only as final tie-breakers in density and invocation fallback routing.
• Add fresh-run --pin-provider <TARGET> plumbing through direct/agent dispatch into routing, with explicit invalid/ineligible pin errors.
• Add focused live-load, stale-row, placement-pin, and CLI parser tests; update source guards and role/intrinsic metadata for touched surfaces.

Verification

• cargo fmt --check (/tmp/age35-gate.YwuH/cargo-fmt-check-4.log)
• cargo clippy --workspace --all-targets -- -D warnings (/tmp/age35-gate.YwuH/cargo-clippy-6.log)
• cargo test --workspace (/tmp/age35-gate.YwuH/cargo-test-workspace-4.log)
• Focused behavior/runtime: runtime-balancer-tests-3.log, cargo-test-runtime-2.log

Audit

Final six LOW verdicts in /tmp/age35-gate.YwuH:

• proof-risk: audit4-proof-risk.log
• coverage: audit4-coverage.log
• coupling: audit4-coupling-rerun.log
• cohesion: audit4-cohesion.log
• pattern: audit4-pattern.log
• process-tree: audit4-process-tree.log