Accept both release archive shapes

[myobie]

Result

The updater accepts exactly two valid archive shapes: fabric alone, or the fabric and fabric-sync pair.

Release 0.2.4 publishes a canonical paired archive for 0.2.2 readers. It also publishes a distinct fabric-only archive for Bluey's strict 0.2.1 reader.

A fabric-only install removes an installed companion and keeps the prior pair for rollback. Extra, missing, duplicate, and dot-prefixed members remain errors.

The explicit URL route still does not check Git direction or an expected version. Silber.cos will verify the literal URL and checksum against the release before Bluey receives them.

Proof

• The one-member reader test failed before the change.
• The dual-shape workflow test failed before the change.
• 517 active library tests passed; 5 measurement tests stayed ignored.
• 19 binary tests passed.
• 8 update command tests passed.
• 11 provisioning tests passed.
• A local release build produced a two-member canonical archive and a one-member compatibility archive.
• Both local binaries reported version 0.2.4.

Release boundary

No release or deployment is part of this pull request. Silber.cos owns both gates.