[TASK] Remove the deprecated aura-web-server binary #540

Outcome

aura is the only executable AURA builds, ships, and packages. The aura-web-server binary and every artifact derived from it are gone.

Context

The unified binary landed in #409 / PR #539. aura-web-server remains as a thin shim that prints a deprecation warning and delegates to the same entry point aura webserver uses. It links the full server library, so every release and the published image carry a second binary of nearly the same size as aura.

This is the final removal step of the compatibility window defined in #410, tracked separately so it can be scheduled into a breaking release on its own.

Scope

• Remove the aura-web-server binary target and the tests covering the shim. The aura-web-server crate and its library remain.
• Remove the binary from the build, container, release-artifact, and packaging paths.
• Update any remaining references so nothing in the repo builds, verifies, distributes, or invokes it.
• Publish the removal in release notes alongside the migration guidance from [FEATURE] Retire aura-webserver with a compatibility transition #410.

Acceptance criteria

• A release build produces exactly one executable per platform, and artifact verification passes against the reduced set.
• The published container image contains only the aura binary.
• Only the aura package is published.
• No in-repo build, deployment, packaging, or test path references the aura-web-server binary.
• Ships as a breaking change (! and a BREAKING CHANGE: footer) in a release whose notes state the replacement command.

Dependencies

Blocked by the compatibility window in #410 — do not merge before it closes.

Parent epic: #353
Initiative: #370