fix: updates Tack pin to v1.0.0

[kalyanoliveira]

Summary

Updates the pinned Tack fallback package to Tack v1.0.0.

What changed

• Replaces the old Tack source tarball pinned to commit
  8c574901340af860979500f24495417ce7e53cdc with the v1.0.0 release
  tarball.
• Updates the source hash accordingly.

Why

The old Tack revision depends on git2/libgit2-sys. Its libgit2-sys
version requires libgit2 >= 1.9.3, while nixpkgs can sometimes provide
libgit2 1.9.2 (this was the case with me: I created a thread about this on
Zullip, but no replies. Hence, PR). Because that old Tack package sets
LIBGIT2_NO_VENDOR, the build fails instead of falling back to vendored
libgit2.

Tack v1.0.0 has moved away from git2/libgit2-sys and builds successfully
in this environment.

Testing

nix-shell ./dev/bootstrap-tests.nix --run test-all

Result on this branch:

• Tack builds successfully.
• test-tack passes.
• test-write-lock-tack passes.
• The full suite still fails at test-write-lock-npins because of a separate
  npins fixture issue fixed in the follow-up PR
  test/npins-lock-fixture-version.

Targeted Tack smoke test:

nix-shell -E '
let
  pkgs = import <nixpkgs> { };
  ff = import ./. { inherit pkgs; modules = {
    inputs.empty.url = "github:vic/empty-flake";
    outputs = _: { };
  }; };
in
pkgs.mkShell {
  buildInputs = [ (ff.flake-file.apps.write-tack pkgs) ];
}
' --run 'write-tack --help || true'

Result: passed.

Feel free to verify results for yourself.

Related work

This PR intentionally fixes only the Tack package compatibility issue. The full
set of related changes has also been validated together on the integration
branch:

chore/integration-verify-bootstrap-fixes

That integration branch includes this PR plus the standalone writer target,
npins fixture, and bootstrap argument work that I did.