release(v1.7.1-alpha): version bump for end-to-end OTA test

Trivial bump on top of df83163f. No code changes — this exists purely so
the fleet nodes now sitting on 1.7.0-alpha have a real target to exercise
the OTA pipeline against: check → download → apply → restart → state
reconciliation. The binary content differs only in the embedded
CARGO_PKG_VERSION string.

Frontend tarball reused from v1.7.0-alpha (same bytes, copied to a new
filename to match the manifest component name convention).

Artefacts:
  archipelago                                     7f7981bd…56eef0  40391760
  archipelago-frontend-1.7.1-alpha.tar.gz (dup of 1.7.0)  dc3b63af…e9a8370  76984288

Manifest changelog is a single plain-language sentence explaining that
this is the test release — per the saved feedback about keeping
fleet-facing strings readable.

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 = "1.7.0-alpha"
+version = "1.7.1-alpha"
 dependencies = [
  "anyhow",
  "archipelago-container",

core/archipelago/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "archipelago"
-version = "1.7.0-alpha"
+version = "1.7.1-alpha"
 edition = "2021"
 description = "Archipelago Bitcoin Node OS - Native backend"
 authors = ["Archipelago Team"]