release(v1.7.21-alpha): operator-editable FIPS seed anchors

Adds a local seed-anchor list at <data_dir>/seed-anchors.json. Each
entry is {npub, address, transport, label}. On archipelago startup
and every 5 minutes the list is pushed into the running fips daemon
via `fipsctl connect <npub> <addr> <transport>`, so a cluster can
anchor itself independently of the global fips.v0l.io. A flaky or
unreachable public anchor no longer strands a fresh install.

New RPCs:
- fips.list-seed-anchors
- fips.add-seed-anchor (validates npub1… + host:port)
- fips.remove-seed-anchor
- fips.apply-seed-anchors (on-demand re-dial)

New standalone UI card at views/server/FipsSeedAnchorsCard.vue. Not
wired into Home.vue / Server.vue — operator places it per the
entry-point convention.

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

core/archipelago/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "archipelago"
-version = "1.7.20-alpha"
+version = "1.7.21-alpha"
 edition = "2021"
 description = "Archipelago Bitcoin Node OS - Native backend"
 authors = ["Archipelago Team"]