Attach standalone binaries to GitHub releases #134

From discussion #108 (ilbertt, nibrun one-click deploy presets).

Request: ship a Linux amd64 binary (or .tar.gz) with SHA-256 checksum as release assets, so Calnode can run outside Docker and downstream presets (nibrun catalogue alongside PocketBase/Gitea/Memos) can deploy from an upstream download instead of maintaining their own build.

Current state: releases carry zero assets — gh release view v0.10.0 --json assets is empty. docker-publish.yml builds multi-arch images and cuts the GitHub Release on vX.Y.Z tags, but attaches no binaries.

Scope questions for whoever picks this up:

• Which targets? Minimum linux/amd64; consider linux/arm64 to match the Docker matrix.
• Static binary feasibility: cgo/SQLite build (modernc.org/sqlite is pure Go, but confirm no cgo leaks in), plus the frontend is go:embed-ed so the binary is self-contained already.
• Checksum file + docs note (README/DEPLOY) with the "Deploy on nibrun" button ilbertt offered.
• Confirm with ilbertt in Publish standalone binaries with GitHub releases #108 what artifact shape his preset needs before building.

Maintainer already replied in #108 (2026-09-30) saying yes in principle. Keep that thread updated.

Discussion: #108