fix(reset): address review and self-runner test failures

[genedna]

What

• Fix the self-hosted compat-offline-core failure by giving the cloud object-restore unit tests an isolated Libra repo/current-directory context before they call restore logic that checks obliteration tombstones.
• Address the fix(reset): support git-style bare path reset #431 review comment by preserving the user-provided -- separator when rewriting libra reset -- <pathspec> args, so dash-prefixed filenames like -h and --help remain pathspecs instead of flags/help.

Why

The cloud tests were assuming the process cwd was already a Libra repository. That is false in GitHub Actions self-hosted runner checkouts, which are ordinary Git worktrees. The reset rewrite also dropped clap's positional separator, changing parsing for dash-prefixed pathspecs.

Checks

• cargo +nightly fmt --all --check
• LIBRA_SKIP_WEB_BUILD=1 cargo test --test command_test command::reset_test::reset_ -- --nocapture
• LIBRA_SKIP_WEB_BUILD=1 cargo test --lib cloud_restore_indexed_objects -- --nocapture
• cargo clippy --all-targets --all-features -- -D warnings

Note: this PR is stacked on #431 (codex/reset-bare-path-git-compat) so it only contains the two follow-up fixes.

[Copilot]

Pull request overview

This PR fixes two regressions impacting reliability and Git-compat CLI behavior: (1) unit tests for cloud object restore now run inside an isolated Libra repo/CWD so they don’t depend on the runner’s checkout context, and (2) libra reset -- <pathspec> rewrites now preserve the user-provided -- separator so dash-prefixed filenames remain pathspecs (not flags/help).

Changes:

• Preserve -- when rewriting libra reset -- <pathspec> argv so -h / --help can be treated as filenames after the separator.
• Add an integration regression test covering dash-prefixed pathspecs passed after --.
• Stabilize cloud restore unit tests by entering an isolated repo + HOME/LIBRA_TEST_HOME context and running these env/CWD-mutating tests under #[serial].

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/command/reset_test.rs	Adds regression coverage ensuring reset -- <dash-prefixed> is treated as a pathspec and unstages correctly.
src/command/cloud.rs	Adds a test helper to enter an isolated Libra repo/CWD + HOME context; marks affected async tests #[serial] to avoid cross-test interference.
src/cli.rs	Fixes reset argv rewriting to re-insert -- before forwarding the original post-separator pathspecs.