Bound repository scans and align maintenance checks

[EpochTX]

Changes

• Limit concurrent instruction-file reads to 16 while preserving deterministic result order.
• Count per-file findings in one pass instead of filtering every issue for each file.
• Extend the 120-file performance guard to verify per-file finding totals.
• Remove the obsolete test requiring scheduled Dependabot updates and document manual dependency maintenance with Node 20 compatibility checks.

Scheduled Dependabot version update PRs were disabled separately on main in ce75174.

Validation

• ESLint, Prettier, TypeScript, and all 75 tests passed locally.
• 17-case rule benchmark passed with 100% precision, recall, and coverage; built CLI contract passed.
• 120-file performance guard passed: 650.3 ms, 117 MiB, 1,440 findings.
• The combined pnpm verify script hit a local tsx IPC EPERM on the benchmark step; the same benchmark and subsequent checks passed via node --import tsx. GitHub CI will run the standard commands.