Seal prepared request capabilities for v0.4.4

[0xmrma]

Summary

• seal the final HTTPX request and capability metadata before budget reservation, then revalidate both immediately before network I/O
• bind prepared capabilities to one adapter and observation session, make them single-use, and reject content/stream divergence
• reject mixed-dimension header mutations and unsupported mutation families
• make journal mutation-delta identifiers run-local and synchronize the documented API, budget, evidence, and validation contracts
• bump the maintained release baseline to 0.4.4

Validation

• 348 tests pass
• critical-module branch coverage: 94.89%; corrected core: 86.64%; transport: 93.99%
• 39/39 committed policy mutants killed
• 22/22 deterministic benchmark cases pass across 942 attempts
• Ruff, enforced mypy scopes, compileall, pip check, and pip-audit pass
• wheel and sdist pass twine validation; clean-wheel install reports 0.4.4 and includes all packaged schemas and benchmark data