feat: architecture review fixes, self-update system, CI pipeline, supply chain hardening

Architecture review (all P0+P1 issues now fixed):
- Add 10s timeout to 6 bare Nostr client.connect() calls
- Pin all 12 crypto deps to exact versions from Cargo.lock
- Pin all 15 floating container image tags to exact patch versions
- Add CI pipeline (cargo fmt + clippy + tests, frontend type-check + build)

Self-update system (git.tx1138.com):
- scripts/self-update.sh: pull, build, install, restart with rollback
- systemd timer checks daily at 3 AM
- update.check RPC does git-based checks when repo is present
- update.git-apply RPC triggers self-update from UI
- Default update URL changed from GitHub to git.tx1138.com
- Git added to ISO package list for fresh installs

Documentation:
- CHANGELOG v1.3.1 with all changes
- README updated (version, update system section)
- BETA-PROGRESS session #6 logged
- architecture-review.html: 4 issues marked FIXED, 8/12 refactoring done

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/dispatcher.rs

@@ -308,6 +308,7 @@ impl RpcHandler {
             "update.dismiss" => self.handle_update_dismiss().await,
             "update.download" => self.handle_update_download().await,
             "update.apply" => self.handle_update_apply().await,
+            "update.git-apply" => self.handle_update_git_apply().await,
             "update.rollback" => self.handle_update_rollback().await,
             "update.get-schedule" => self.handle_update_get_schedule().await,
             "update.set-schedule" => {