fix(discovery): canonical pay invocations in skill.md (1.3.6)

[vvillait88]

Summary

• build_skill_md per-rail compatibility notes referenced agentscore-pay --chain <chain> as a usage hint, but --chain is a flag of the pay / balance / fund subcommands, not a top-level option. Bare agentscore-pay --chain X is not a valid invocation; the canonical form is agentscore-pay pay --chain X.

• Corrects the solana_mpp note: previously claimed X-Payment header carries the signed credential, but Solana MPP solana/charge carries the credential in Authorization: Payment (same as Tempo MPP). Brings the python skill.md output into parity with the node-commerce 1.3.3 sibling and matches the actual implementation.

• Normalizes the x402_base note to the same agentscore-pay pay --chain base shape as the other rails (was bare agentscore-pay).

• Bumps to 1.3.6 with in-range dep refresh:

  markdown-it-py 4.0.0 -> 4.1.0
  pydantic       2.13.3 -> 2.13.4
  pydantic-core  2.46.3 -> 2.46.4
  ujson          5.12.0 -> 5.12.1
  

  All top-level deps are already at the latest published version on PyPI (httpx 0.28.1, x402 2.9.0, pympp 0.7.0, cdp-sdk 1.44.0).

Test plan

• uv run ruff check . clean
• uv run ruff format --check . clean
• uv run ty check agentscore_commerce/ clean
• uv run pytest -q --no-cov 724 pass / 3 skipped / 0 fail
• Lefthook pre-commit (ruff) and pre-push (ty + vulture) both pass
• CI green
• Tag v1.3.6 after merge to trigger PyPI trusted publish

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