Publish rolling :edge and immutable :sha-<commit> container images on merge to main

[siavashhub]

Summary

Publishes container images on every merge to main, to provide ability to pin fixes that are merged but not yet part of a tagged release.

Closes #2372.

What changed

.github/workflows/build-and-push-container.yml:

• Added a push trigger for the main branch (alongside the existing v*
  tag trigger).
• Merge to main now publishes:
  • :edge a rolling tag that always points at the latest main build.
  • :sha-<short> an immutable, per-commit tag for reproducible pinning.
• Tag release (v*) behavior is unchanged: publishes :vX.Y.Z + :latest.
• Manual dispatch behavior is unchanged: builds the given tag and moves :latest only when add_latest is checked.

Tagging matrix

Trigger	Tags published	Moves latest?
Push to main	edge, sha-<short>	No
Push tag vX.Y.Z	vX.Y.Z, latest	Yes
workflow_dispatch	<input.tag> (+ latest opt.)	If add_latest

[siavashhub]

@jeremyfowers ready for merge