release: 0.4.0 — ship the x402 v2 client to PyPI

PyPI has carried 0.3.1 since 2026-07-09, which predates the canonical
x402 v2 migration (46b74b7, 2026-08-12). The live manifest at
app.suedeai.ai/.well-known/x402.json advertises x402Version 2, so every
'pip install suede-ai' has been handing users a v1 client against a v2
API. Three commits sat unreleased.

Minor bump rather than patch: the v2 migration changed the client surface
and the package exports.

34 tests pass; both distributions build clean.

chore: bump version to 0.3.1

Docs-only functional diff, but PyPI bakes README/description into
package metadata at publish time — 0.3.0's published page still says
'3 paid resources' despite the README fix landing on GitHub. Bumping
so the corrected docs (20 verified live endpoints) actually reach
PyPI. Also fixes the same understatement in the module docstring and
syncs the User-Agent string.

Merge remote-tracking branch 'origin/main'

feat: add 5 new endpoints, bump to v0.2.0

Add prompt_analyze, chain_chat, rig_analyze, rig_oracle, rig_roast to
bring the public surface to 22 methods matching the live x402 manifest.

Update version, description, User-Agent header, and test parametrize
list to reflect 22 endpoints throughout.