release(v1.7.12-alpha): bump on top of working-OTA 1.7.11

Version-only bump. Sits above v1.7.11-alpha which user has verified
runs the full Install Update pipeline end-to-end (check → download
→ install → auto-restart). Freshly-installed nodes from the 1.7.11
ISO will see 1.7.12 as their first OTA target.

Frontend tarball byte-identical to v1.7.11 (same sha).

Artefacts:
  archipelago                                      247f65c2…54f40df9  40385472
  archipelago-frontend-1.7.12-alpha.tar.gz         0644a436…54f58    76983846 (reused)

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 = "1.7.11-alpha"
+version = "1.7.12-alpha"
 dependencies = [
  "anyhow",
  "archipelago-container",

core/archipelago/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "archipelago"
-version = "1.7.11-alpha"
+version = "1.7.12-alpha"
 edition = "2021"
 description = "Archipelago Bitcoin Node OS - Native backend"
 authors = ["Archipelago Team"]