Improve JS/TS comment filtering

[Vladyslav-Kuksiuk]

This PR:

• improves JS/TS comment filtering;
• splits the filtering tests into smaller, language-specific files.

Resolves this issue.

[Copilot]

Pull request overview

This PR introduces a dedicated JavaScript/TypeScript comment filter to avoid stripping comment-like text inside template literals and regex literals, addressing the regression described in issue #67.

Changes:

• Added a new JavaScriptCommentFilter with JS/TS-aware scanning for template literals (including ${...}) and regex literals.
• Switched .js/.jsx/.ts/.tsx filtering from the generic marker-based filter to the new JS/TS filter and removed the old JS marker config.
• Expanded the JS/TS test suite with cases covering templates, nested templates, and regex literals.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
embedding/commentfilter/javascript_filter.go	New JS/TS-specific lexical scanner to strip real comments while preserving template/regex literal content.
embedding/commentfilter/config.go	Registers JavaScriptCommentFilter for JS/TS extensions and removes the old jsSyntax marker configuration.
embedding/commentfilter/filter_test.go	Adds JS/TS regression tests for templates, nested templates, and regex literals.