Add MIT license and finalize source-publication readiness

[KulmanD]

What changed

• add the canonical MIT License for Copyright (c) 2026 Denis Kulman
• add a root security policy covering supported source and private vulnerability reporting
• replace the obsolete release badge/link with an MIT badge and source-first installation guidance
• update the publication-readiness report with completed owner decisions, live GitHub controls, exact obsolete release inventory, and separate source/binary readiness

Why

The source repository needs clear redistribution terms, a security reporting policy, generic current configuration naming, and a publication checklist that does not present historical ad-hoc binaries as current downloads.

Validation

• git diff --check
• generated-default verification
• shell syntax checks for archive/release scripts
• fresh source archive extraction and content scan
• confirmed LICENSE, SECURITY.md, and config/defaults.json are included
• confirmed no retired configuration string or owner home path appears in the source archive
• swift build
• swift build -c release
• verified helper size remains 433,528 bytes and __TEXT remains 212,992 bytes
• verified release helper does not link XCTest or Testing

Local swift test cannot import XCTest from the installed Command Line Tools. The required GitHub Actions macOS workflow is the authoritative full test run for this PR.

Risks and limitations

• no Swift runtime source, configuration behavior, tests, or packaging scripts changed
• no release, tag, repository setting, visibility setting, or binary was changed or published
• deletion of the obsolete v0.2.0 and v0.3.0 GitHub release entries remains pending explicit owner confirmation
• GitHub license detection must be confirmed after merge because the repository license endpoint evaluates the default branch