chore: add CI and document Augur's alpha trust boundary

[DivyamTalwar]

Summary

• add pinned GitHub Actions gates for frontend lint/build and Rust format/clippy/tests
• label Augur OS as alpha/workspace branding until signed distribution and an extension platform exist
• correct verifier language: current verification is bounded to specialist-supplied evidence metadata
• document Claude/Apollo data egress, credential storage limits, and remove broken release-film links

Verification

• git diff --check
• Local Bun/Rust execution was unavailable in the authoring environment; the new CI is the authoritative build/test gate.

Security

No application secrets or provider behavior changed. Documentation now describes the real data boundary.