Bump all SDKs to 0.21.0

[etbyrd]

Summary

Cut the 0.21.0 release across all three SDKs.

First release that ships dual-host routing for /send-mail (introduced in #59):

• /send-mail routes to api.primitive.dev/v1 automatically (Cloudflare Worker, attachments up to 30 MiB raw).
• Every other operation continues to hit primitive.dev/api/v1.
• Customers don't see the split. PrimitiveClient.send / .Send is the single entry point.

Stale CLI credentials from any prior version are auto-cleared with a 'you've been logged out, please re-login' notice; users on upgrade run primitive login once and continue.

Touches only the three version-of-record files plus the uv lock entry.

Test plan

• make node-check (lint, typecheck, 654 tests, generated-file sync)
• make go-check (vet, fmt, tests)
• make python-check (ruff, basedpyright, 226 tests)

Should be rebased onto main after #59 lands; merging this PR tags + publishes via the existing release flow.

[greptile-apps]

Greptile Summary

Bumps all three SDKs (Go, Node, Python) from 0.20.0 to 0.21.0, the first release shipping dual-host routing for /send-mail (introduced in #59). The uv.lock update also adds previously missing platform wheels for cffi and cryptography on ppc64le and s390x architectures.

• sdk-go/VERSION, sdk-node/package.json, sdk-python/pyproject.toml: single-line version bump in each.
• sdk-python/uv.lock: version entry updated and new platform-specific wheels added for cffi 2.0.0 and cryptography 46.0.6, expanding the set of supported architectures.

Confidence Score: 5/5

Safe to merge — all four files are version-of-record updates with no functional logic changes.

The change is limited to bumping three version strings and refreshing the uv lock file with additional platform wheels. No application logic, API surface, or security-sensitive code is touched.

No files require special attention.

Important Files Changed

Filename	Overview
sdk-go/VERSION	Version bumped from 0.20.0 to 0.21.0
sdk-node/package.json	Version bumped from 0.20.0 to 0.21.0
sdk-python/pyproject.toml	Version bumped from 0.20.0 to 0.21.0
sdk-python/uv.lock	Version bumped to 0.21.0; additional platform wheels added for cffi and cryptography (ppc64le, s390x architectures)

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into bump-sdks-to-0...." | Re-trigger Greptile}