termux: declarative ~/.ssh/config + termux-api package

- home/termux.nix: programs.ssh.settings with the 7 known hosts
  (replaces hand-copied ~/.ssh/config; ssh aliases z-s/z-st/z-o/z-ot
  removed, lamet/pubray-1 kept since they have no Host entry)
- modules/termux/termux-api.nix: build termux-api 0.59.1 (cmake,
  am resolved from PATH, shebangs fixed); adds termux-battery-status,
  termux-notification, termux-clipboard-*, etc. Needs the Termux:API
  Android app (com.termux.api from F-Droid) as the actual backend
- mobile.nix: enable android-integration.am (termux-am backend for am)

configurations/mobile.nix

@@ -105,6 +105,9 @@ let
       time.timeZone = "Europe/Moscow";
 
       android-integration.termux-setup-storage.enable = true;
+
+      # Provides `am` (termux-am) — required by termux-api's broadcast backend.
+      android-integration.am.enable = true;
     };
 in
 inputs.nix-on-droid.lib.nixOnDroidConfiguration {