chore: rename drift-labs GitHub URLs to velocity-exchange

[ChesterSim]

Part of renaming the GitHub org drift-labs -> velocity-exchange.

DRAFT — do not merge until the velocity-exchange org (and, where applicable, the @velocity-exchange npm scope) exists; old URLs currently redirect.

URL forms changed

• github.com/drift-labs/ → github.com/velocity-exchange/ (3 occurrences: mkdocs.yml repo_url, pyproject.toml homepage, vaults SDK reference links)
• drift-labs.github.io → velocity-exchange.github.io (2 occurrences: mkdocs.yml site_url, pyproject.toml documentation)

Total substitutions: 7 across 4 files

Files changed

• mkdocs.yml — repo_url, repo_name, site_url
• pyproject.toml — homepage, documentation URLs
• src/driftpy/vaults/__init__.py — drift-vaults repo reference in docstring
• src/driftpy/vaults/helpers.py — drift-vaults repo reference in docstring

Skipped (upstream-Drift historical refs)

• .gitmodules:3 — submodule URL https://github.com/drift-labs/protocol-v2.git: this is the fork-origin upstream submodule pointing to the original Drift protocol-v2 repository; left as-is to preserve the upstream reference.
• README.md:10 — link https://drift-labs.github.io/v2-teacher/: this points to the Drift Labs upstream documentation site ("v2-teacher"), which is a separate Drift project resource, not this repo's own docs site.

Notes

No @drift-labs/* npm-scope deps or imports were present in this Python repository — no npm scope warning applies.