feat: validate only commits not yet on any remote

[agherzan]

When pushing a new branch, the pre-push hook derived its base from a
single remote's HEAD. If that remote was behind (e.g. a fork whose main
is a stale copy of upstream), it re-validated commits already reviewed
and merged elsewhere, and could reject a push over commits the author
never touched.

Base validation on every remote-tracking ref instead: a commit already
present on any remote has been published and does not need rechecking.

Excluding a set of refs rather than a single base also lets the root
commit be validated, which a single exclusive base can never reach.

Closes: #10

[Copilot]

Pull request overview

This PR updates gitlance’s local-hook workflow to avoid re-validating already-published commits by validating only commits not yet reachable from any remote-tracking ref, and adds a commit-msg hook path via --message-file validation (addressing Issue #10’s root-commit validation gap).

Changes:

• Add --not-on-remotes mode to validate commits reachable from --head but not from any remote-tracking ref, with a clean success when there’s nothing new to check.
• Add --message-file mode to validate a single commit message file (for commit-msg hook usage), including git-like comment/scissors stripping.
• Update hooks/tasks/tests/docs to support the new CLI behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/integration_tests.rs	Refactors test runner to capture process output; adds integration coverage for --not-on-remotes and --message-file.
Taskfile.yml	Installs the new commit-msg hook alongside pre-push.
src/main.rs	Adds new CLI flags and routes execution into message-file, not-on-remotes, or base/head range modes.
src/lib.rs	Re-exports new git helpers used by the CLI.
src/git.rs	Adds remote-tracking ref enumeration, commit selection via exclude sets, and commit-message parsing utilities + unit tests.
README.md	Documents direct CLI usage, including --message-file and --not-on-remotes.
githooks/pre-push	Switches new-branch behavior to --not-on-remotes while keeping existing-branch merge-base behavior.
githooks/commit-msg	New hook that validates the commit message file via --message-file.

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[jw-can]

LGTM, nice and clean!
My only comment for potential future work: There's diverging code paths depending on arguments of the same command. Could the strategy design pattern help with organizing this?