Adds docs/ARCHITECTURE.md (module layering, foundational infra decisions,
subsystem index) and docs/REALTIME_SESSION.md (the WS relay design, the
provider extensibility seam, the trust boundary, SvelteKit's WS plumbing
workaround, and the OpenAI event-naming gotcha found via live testing).
Restructures AGENTS.md around orientation, conventions, and process, and
establishes documentation as part of the same change as the work itself
rather than a follow-up pass.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Jonathan Hinkel