Feature request: Expose HackMD comments through the API and MCP

I want to use HackMD as the review interface for content stored in Git.

Git is the single source of truth. An automated process updates the HackMD note from the repository, reviewers leave comments in HackMD, and an agent processes those comments into a GitHub pull request.

HackMD currently supports programmatic note updates, but comments are not available through the public API, CLI or MCP.

## Desired workflow

1. Content is pushed from Git to an existing HackMD note.
2. Reviewers leave paragraph or text-selection comments.
3. An agent retrieves open comments.
4. The agent classifies comments as:

* safe to action automatically;
* requiring clarification;
* requiring operator review;
* not actionable.
5. The agent applies appropriate changes on a Git branch and creates a pull request.
6. The operator reviews and merges the pull request.
7. The merged content is pushed back to HackMD.
8. Actioned comments are resolved.
9. Remaining comments stay open for later review.

## Required capabilities

Please expose note comments through the public API and HackMD MCP.

The integration needs to:

* list comments for a note;
* filter open, resolved or recently updated comments;
* retrieve comment text, replies, author and timestamps;
* retrieve selected text and anchor context;
* identify comments whose anchors are no longer valid;
* reply to comments;
* resolve and reopen comment threads.

Incremental retrieval through webhooks or an `updatedSince` filter would also be useful.

## Suggested MCP tools

```text
list_note_comments
get_note_comment
reply_to_note_comment
resolve_note_comment
reopen_note_comment
```

## Key requirement

Updating an existing note must preserve comment identity.

When a comment can no longer be attached to the current text, the API should return it as detached while preserving the original selected text and surrounding context.

## Why this matters

This would allow HackMD to remain the human-friendly review surface while Git remains authoritative.

HackMD would manage comments and review context. External systems would manage branches, pull requests, automated changes and approvals.

Start in the hackmd-cli code paths for the public API, CLI, and MCP integrations, then compare their existing note-update capabilities with the requested comment workflow. The work is complete when comments can be listed and filtered, their text and anchors retrieved, replies managed, threads resolved or reopened, and comment identity preserved across note updates.

Written by the indexing model from the issue text.