docs: raise v1 review budget to 5,200 lines

[BenWestgate]

Maintainer authorization now allows the v1 installed-package review budget to increase from <5000 to <5200 rather than performing a riskier pre-release refactor solely to recover ~100 lines.

This focused policy/enforcement change updates only:

• AGENTS.md
• docs/developer/api.md
• test_production_size_budgets_are_enforced

The current reviewability-v1 package measures 4,893 nonblank/noncomment Python lines with the same recursive counter. The previously simulated combined v1 stack measured ~5,102, leaving ~98 lines of headroom under the authorized cap.

Local verification:

• git diff --check
• exact production-line counter: 4,893 < 5,200

The full repository test suite is delegated to PR CI because the local system Python lacks the pinned test-only bip32/coincurve oracle dependencies.

This supersedes issue #61's earlier no-budget-increase condition following explicit maintainer authorization.

Closes #61