docs: pivot deployment target from K8s container to native desktop app

[IamMrCupp]

Closes #28.

Summary

• Rewrites DEPLOYMENT.md around native desktop GUI app distribution (macOS Apple Silicon primary; macOS Intel + Linux x86_64/ARM64 tested; Windows out of scope for v1).
• Old Kubernetes / Docker content moved verbatim into an Archived approaches: Kubernetes appendix at the bottom of DEPLOYMENT.md, with a clear status note and the rationale for the pivot (Audiophore lives next to Synesthesia + the lighting LAN; orchestration adds nothing the constraints can use).
• Docker / OCI container packaging is kept as a deferred future option (dev environments / M4+ appliance image), not the primary path.
• GUI framework choice (Tauri / egui / Iced / Slint / Dioxus / Xilem) is flagged as a follow-up research artifact — does not block M1 engine/adapter work. Downstream decisions in SESSION_HANDOFF.md (axum, Svelte + Tailwind) and RUST_ECOSYSTEM.md UI build pipeline are annotated as contingent on that choice.
• SESSION_HANDOFF.md Locked decisions table updated: new rows for deployment target, container packaging, GUI framework, show file storage. Identity & infrastructure clarifies the K8s cluster's role is now marketing-site-only.
• README.md deployment-target line and doc-index summary updated.
• HARDWARE.md Workspace setup swaps the "your K8s cluster has capacity" suggestion for the actual in-house dev/test hardware (Ubuntu server, Pi 5, Le Potato, Intel Mac).
• IMPLEMENTATION_PLAN.md CI matrix bullet updated to reflect the four-target shape (macOS aarch64/x86_64 + Linux x86_64/aarch64) on native GitHub runners; Windows removed.
• RUST_ECOSYSTEM.md cross-compile section reflects native ARM runners; if-addrs note no longer references K8s nodes.

Out of scope (follow-up issues)

• GUI framework selection (research artifact + PR).
• Concrete native packaging tooling (tauri-bundler vs cargo-bundle vs framework-specific) — gated on framework choice.
• Auto-update strategy.
• Working-folder docs (CONTEXT.md, bench-pod.md, research.md) — outside this repo; updated separately.

Test plan

• CI green (markdown-lint, link-check, etc.)
• Render DEPLOYMENT.md on GitHub — confirm the in-page anchor #archived-approaches-kubernetes resolves and the appendix scrolls cleanly.
• Cross-reference check: no doc outside DEPLOYMENT.md's archived appendix asserts K8s as the deployment target.