release(v1.6.0-alpha): smoke-test release for system-update flow

No functional changes from v1.5.0-alpha — this release exists only to
validate the in-app update pipeline end-to-end (manifest check → staged
download → apply → restart → version bump in UI sidebar).

Dropping just the manifest + artifacts; no manual deploy to the fleet.
.116/.228/.253 should notice within 30 min (periodic update-check
interval) and surface the update in the dashboard.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/Cargo.lock

@@ -80,7 +80,7 @@ checksum = "a23eb6b1614318a8071c9b2521f36b424b2c83db5eb3a0fead4a6c0809af6e61"
 
 [[package]]
 name = "archipelago"
-version = "1.5.0-alpha"
+version = "1.6.0-alpha"
 dependencies = [
  "anyhow",
  "archipelago-container",

core/archipelago/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "archipelago"
-version = "1.5.0-alpha"
+version = "1.6.0-alpha"
 edition = "2021"
 description = "Archipelago Bitcoin Node OS - Native backend"
 authors = ["Archipelago Team"]