fix: lint comments after shebangs

[lawrence3699]

Disclaimer: This PR was authored by an agent and reviewed against the reproduced issue and local test results.

Fixes #962.

Before this change, CommentMasker ignored any merged comment span that started with a shebang. When tree-sitter merged the first-line shebang with the following comment block, the later comments were skipped too.

This change only strips the first line of a real shebang at the start of the file, then keeps linting the rest of the merged comment span.

How I tested this:

• cargo test -p harper-comments
• cargo run -q -p harper-cli -- lint /tmp/harper-962-with-shebang.sh --count --no-color
• cargo run -q -p harper-cli -- lint /tmp/harper-962-no-shebang.sh --count --no-color
• cargo run -q -p harper-cli -- lint /tmp/harper-962-fake-shebang.sh --count --no-color

[Copilot]

Pull request overview

Fixes #962 by ensuring CommentMasker no longer drops an entire merged comment span when it begins with a shebang; instead it strips only the first-line shebang at the start of the file and continues linting subsequent comments.

Changes:

• Update CommentMasker::create_mask to trim a leading first-line shebang (only when span.start == 0) rather than ignoring the entire merged span.
• Add a regression fixture (issue_962.sh) and corresponding test expectation to ensure comments after a shebang are linted.

Reviewed changes

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

File	Description
harper-comments/src/masker.rs	Adjusts masking logic to trim only the initial shebang line (if present at file start) while preserving linting of subsequent merged comment content.
harper-comments/tests/language_support_sources/issue_962.sh	Adds a shell script fixture reproducing the shebang+comment scenario from #962.
harper-comments/tests/language_support.rs	Registers the new fixture in the language support test suite with the expected lint count.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[elijah-potter]

This looks like a simple enough change to me. Thanks!