fix(converter): emit > **MARKER** form to close admonition round-trip

[pchuri]

Description

Closes #135.

storageToMarkdown emitted the bare [!info] shorthand for callout macros, but the bare form has no explicit body terminator. A blank line inside a multi-paragraph body is therefore indistinguishable from the body ending, so re-uploading downloaded markdown silently dropped every paragraph after the first — content escaped the macro on round-trip.

Reproduction (pre-fix)

Author writes the README-recommended form:

> **INFO**
> foo
>
> bar

markdownToStorage correctly puts both paragraphs inside <ac:rich-text-body>.
storageToMarkdown then collapses to:

[!info]
foo

bar

Re-uploading hits lib/macro-converter.js's preprocessor (?=\n\s*\n|...) lookahead, which treats the blank line as the end of the body. <p>bar</p> lands outside the macro.

Fix

Switch the storage→markdown output to the > **MARKER** blockquote form that README already documents as the canonical authored shape. The > prefix gives the body an explicit boundary, so markdownToStorage — which already handles this form correctly via the blockquote handler (PR #132) — preserves every paragraph on re-upload.

markdownToStorage still accepts the bare [!marker] form on input for backwards compatibility with already-downloaded files.

The three near-duplicate per-marker handlers (info / warning / note) collapse into a single CALLOUT_MARKERS loop, matching the pattern already used elsewhere in this file (PRs #132 and #134).

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature
• Breaking change
• Documentation update

Testing

• Tests pass locally with my changes (391 passing, was 385)
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes

6 new tests in a storageToMarkdown callout round-trip describe block:

• info / warning / note macros emit the > **MARKER** form (3 tests)
• Multi-paragraph body separates paragraphs with > lines (issue [BUG/DISCUSS] Admonition body multi-paragraph round-trip drops content outside the macro #135 direct repro)
• Full round-trip (md → storage → md → storage) preserves both paragraphs inside <ac:rich-text-body> and asserts no paragraph escapes the macro
• Single-paragraph round-trip preserves body without leaking marker text

The pre-existing should convert Confluence macros to admonitions test in confluence-client.test.js is updated to assert the new output form.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

Note on relationship to #132 / #134

This is the third bug in the same callout code path:

• fix: strip callout markers and narrow detection to paragraph start #132 fixed marker text leaking into the rendered macro body (input side)
• fix: scope [!info] admonition rewrite to block context #134 fixed the [!info] preprocessor running on tokens it shouldn't (input side, code/heading contexts)
• [BUG/DISCUSS] Admonition body multi-paragraph round-trip drops content outside the macro #135 / this PR fixes the output side emitting a form whose body bounds are ambiguous on re-upload

The author of #135 explicitly noted they discovered the bug while verifying #134.

[pchuri]

Self-review follow-up: adjacency fix added

On re-review, the initial commit had a latent bug: the emitted > **MARKER** blockquote was not wrapped in separator newlines, so an adjacent following <p>after</p> would lazy-continue into the blockquote body on re-upload (markdown blockquotes have no closing delimiter — only a blank line ends them).

Reproduction (pre-followup):

storage:  <p>before</p><macro>foo,bar</macro><p>after</p>
                  ↓ download
markdown: before
          > **INFO**
          > foo
          >
          > bar
          after            ← lazy-continues
                  ↓ re-upload
storage:  <macro>foo, bar+after fused</macro>   ← `after` lands inside!

Follow-up commit (c34b386) wraps the output with leading + trailing \n — same convention code and mermaid macros already use (confluence-client.test.js:893-918). The single \n combines with the single \n that htmlToMarkdown emits around adjacent <p> tags to produce blank-line separation.

Adds two regression guards in the new callout round-trip describe block:

• full round-trip with surrounding paragraphs preserves macro boundaries
• downloaded markdown has blank lines on both sides of the callout

Also updates the README's reverse-direction documentation to match the new output form. The bare [!info] shorthand is still accepted on input for backwards compatibility with already-downloaded files.

Test count: 391 → 393 passing.

[github-actions]

🎉 This PR is included in version 2.1.3 🎉

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