Take agentscore-py 2.6.0 (#99)

## Summary

Raises the `agentscore-py` floor from `>=2.5.2` to `>=2.6.0`, which is
the release adding the optional `refreshable` field to `CredentialItem`.
Nothing in this library reads that field, so this is a floor bump rather
than a behavior change.

The old floor already resolved 2.6.0, so this does not change what a
fresh install gets today. It states the intended baseline explicitly
instead, which is what stops a consumer pinning an older SDK and getting
a shape this library was not tested against. Matches the node-commerce
change.

Patch bump to 2.5.14.

## Type of change

- [ ] Bug fix (no breaking change)
- [ ] New feature (no breaking change)
- [ ] Breaking change (existing callers must update)
- [x] Docs, tests, or internal maintenance only

## Public API

None. No exported type, signature, or wire-format change in this
package. The SDK's own addition is `NotRequired`, so nothing re-exported
through here changes shape.

A consumer already on `agentscore-py < 2.6.0` will now resolve an
upgrade rather than stay put. That upgrade is itself additive.

## Test plan

`uv run pytest` (1841 pass, 4 skipped, 95.36% against a 95% floor), `uv
run ruff check`, and `uv run ty check` all clean with 2.6.0 installed.
`uv sync --all-extras --all-groups` used throughout so extras and dev
groups resolve.

## Checklist

- [x] Tests cover the new behavior, and the suite passes locally
- [x] Lint, format, and type checks pass
- [x] Docs and README examples updated if the public surface changed
- [x] No secrets, credentials, or personal data in the diff or the tests

Author: vvillait88

pyproject.toml

@@ -4,15 +4,15 @@ build-backend = "hatchling.build"
 
 [project]
 name = "agentscore-commerce"
-version = "2.5.13"
+version = "2.5.14"
 description = "Agent commerce SDK for Python — identity middleware (FastAPI, Flask, Django, AIOHTTP, Sanic, ASGI) + payment helpers + 402 builders + discovery + Stripe multichain. The full merchant-side toolkit for AgentScore-powered agent commerce."
 readme = "README.md"
 license = "MIT"
 requires-python = ">=3.11"
 keywords = ["agentscore", "agent-commerce", "agentic-payments", "402", "x402", "mpp", "machine-payments-protocol", "fastapi", "starlette", "flask", "django", "aiohttp", "sanic", "middleware", "trust", "reputation", "kyc", "identity", "stripe", "tempo", "solana", "base", "ai-agent"]
 dependencies = [
     "httpx>=0.25.0,<1.0.0",
-    "agentscore-py>=2.5.2",
+    "agentscore-py>=2.6.0",
 ]
 classifiers = [
     "Development Status :: 5 - Production/Stable",