music-acquire: add verified cascade and deploy tally 52eff4db

[mecattaf]

What changed

• add the music-acquire package and Home Manager command, with its verified SoundCloud → YouTube → capture acquisition cascade and recorded-fixture tests
• advance the tally input from 78dd4871 to chapter-2 gate revision 52eff4db
• retire git-ai completely from the declarative system: remove its flake input and lock graph, Home Manager packages, and tally gitAi config
• gate both nightly deploy admission and fleet activation on tally campaign quiescent, replacing the dated ladder skip drop-ins with a durable mechanism

Why

Tally's chapter-2 cleanup removed the legacy authorship integration and now rejects the retired gitAi config key. The dotfiles pin and generated host config must advance together so the daemon can boot on the new contract. The quiescence checks ensure the pin cannot move beneath an armed campaign. The music acquisition utility is included as the other already-completed local change requested for this deployment.

Impact

• acquire becomes available in Tom's user profile
• tally runs at 52eff4db without the retired config surface
• git-ai and git-og leave the user profile
• nightly and manually started fleet deploys defer while any campaign registration is armed

Validation

• nix flake check --no-build
• nix build .#checks.x86_64-linux.music-acquire --no-link -L (19 tests)
• nix build .#nixosConfigurations.coordinator.config.system.build.toplevel --no-link -L (including tally's full release test phase and checked config)
• evaluated and inspected both generated ExecCondition entries against the new tally binary