[FEATURE] Publish DEB packages and an APT upgrade path #405

Outcome

A practitioner on a supported Debian or Ubuntu system can install and upgrade AURA through a normal DEB/APT workflow without cloning the repository, building from source, or choosing a GitHub release artifact.

Scope

• Produce versioned DEB packages for supported Debian and Ubuntu releases.
• Make aura available on the user's PATH after installation.
• Provide an APT repository or equivalent supported channel for installation and upgrades.
• Map package versions cleanly to AURA release versions.
• Document installation, upgrade, and removal.
• Fail clearly on unsupported distributions or architectures.

Acceptance criteria

• A fresh supported system can install AURA using the documented package command.
• The installed aura binary runs successfully.
• The same channel upgrades AURA to a later release.
• Package provenance and the corresponding GitHub release are clear.
• The public getting-started path uses this installation method for supported Debian-family systems.

Parent epic: #309
Initiative: #370