feat: add markdown_to_html Handlebars helper

[joeltjames]

Summary

• Adds a markdown_to_html Handlebars helper that converts Markdown to Asana-compatible HTML for use in html_notes fields
• Uses marked to parse Markdown, then applies post-processing to conform to Asana's supported HTML subset: downgrades h3-h6 to h2, strips images, replaces <del> with <s>, removes unsupported attributes, unwraps details/summary blocks, and normalizes table markup
• Adds marked as a production dependency and bumps several @actions/* packages

This address issue #47

[Copilot]

Pull request overview

Adds a new Handlebars helper to convert Markdown into Asana-compatible HTML for html_notes, and updates dependencies/build artifacts to support the feature.

Changes:

• Added markdown_to_html helper using marked + regex post-processing to conform (roughly) to Asana’s HTML subset.
• Added/updated documentation describing usage of markdown_to_html vs sanitize_markdown and notes vs html_notes.
• Added marked dependency, bumped several toolchain deps, updated lockfile and distribution artifacts, and added tests.

Reviewed changes

Copilot reviewed 4 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/expression/helpers.ts	Registers new markdown_to_html helper and implements Markdown→HTML conversion + Asana compatibility post-processing.
tests/expression/helpers.test.ts	Adds coverage for markdown_to_html conversions (headings, lists, links, code, images, details, tables, etc.).
package.json	Adds marked as a production dependency.
bun.lock	Updates resolved dependency graph for marked and @actions/* bumps.
docs/reference/helpers/text-processing.md	Documents markdown_to_html usage and guidance for notes vs html_notes.
dist/licenses.txt	Adds license text for marked into bundled license output.
dist/expression/helpers.d.ts.map	Updates generated declaration map for helper changes.

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