license: relicense to MIT + README consistency

[MattJackson]

Summary

Relicenses basement from AGPL-3.0 to MIT (authorized: the maintainer holds copyright, all deps are permissive, not a fork), plus a small README/docs consistency pass.

Relicense

• LICENSE: full AGPL-3.0 text replaced with the standard MIT license, Copyright (c) 2026 Matthew Jackson.
• Source SPDX headers: none exist in this repo (no SPDX-License-Identifier in any .go, Dockerfile, go.mod, or package.json), so no header edits were needed.
• README: license badge -> [![License: MIT]]; tagline AGPLv3 -> MIT; comparison-table basement cell -> MIT (other projects' AGPL cells left factual); ## License section -> MIT.
• Other current license statements -> MIT: CONTRIBUTING.md, SECURITY.md, SUPPORT.md, .github/DCO.md, .github/ISSUE_TEMPLATE/config.yml, docs/comparison-research.md (basement's own row + prose), and internal/docslint/docslint_test.go (assertion updated so the docs-lint test matches the new MIT wording).

Docs consistency

• Owner casing mattjackson -> MattJackson on repository web URLs and shields.io badges (README, CONTRIBUTING clone URL, docs/deployment/docker.md raw URLs). ghcr.io/mattjackson/basement and all container/image refs left lowercase (registries require it). Go import paths and the go.mod module path (github.com/mattjackson/basement) were left lowercase — they are functional, case-sensitive module identifiers, not web links.
• CI badge: added as the first badge. .github/workflows/quality.yml triggers on push: branches: [main], so the badge is valid.

Intentionally left as-is

• Other projects' genuine AGPL licenses (MinIO Console / OpenMaxIO forks) in the README comparison table and docs/comparison-research.md.
• Historical CHANGELOG.md and docs/release-notes/* / docs/deployment/upgrade.md records of the original MIT -> AGPLv3 relicense — preserved as accurate, dated project history (rewriting them would falsify the record).