fix(commitments): source commitment type tuning from protocol constants

[woahwhattheheck]

Closes #1919

Summary

• restore the protocol-constants service/GET route and client parsing used by the current frontend
• source commitment-type duration, maximum-loss, and early-exit penalty display from the fetched per-type protocol constants
• retain the existing literals only as loading/error fallback values so the create flow remains usable when configuration is unavailable
• avoid recreating the deleted src/app/commitments/page.tsx architecture referenced by the older issue text
• add one focused parser regression for commitment-type protocol tuning

Scope / validation

This is the existing five-file issue-scoped carrier at 01d50e94946573fbe4b7a04721dd2e903db9c7bd, based directly on current master@0d847032ef5862806cbb678f0bca93b6be44fb17 (5 commits ahead, 0 behind at publication fence). Source/readback validation was performed on the exact carrier; no fresh full-suite or hosted-CI-green result is claimed here.

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