fix: encode unsafe characters in markdown link hrefs

[iamsivin]

Description

The PR fixes links with spaces or parentheses in the URL being rendered as raw markdown ([label](url)) after reopening the editor or on the help center.

Cause

The serialized markdown was invalid. CommonMark does not allow raw whitespace or unescaped parentheses inside link destinations, causing downstream renderers to fail parsing the link.

Solution

Percent-encode whitespace and escape parentheses when serializing hrefs. URLs with whitespace now use the standard [label](url) format instead of autolinks, ensuring links survive markdown serialization and rendering correctly.

[sony-mathew]

@iamsivin can you take a look at this review comment:

Findings
[P1] src/schema/markdown/serializer.js:225 still serializes table-cell links with raw mark.attrs.href.
The PR fixes the shared link mark serializer, but serializeCellContent has its own link branch:
[text](${mark.attrs.href})

So links inside article tables still emit invalid markdown when the href has spaces or parentheses. I verified this against PR head a5a2e3f: a table link with https://example.com/a path/foo(bar) serializes as:

| [inside](https://example.com/a path/foo(bar)) | plain |

Parsing that back splits the href at the space and leaves literal markdown in the cell. Chatwoot’s help-center renderer also renders it literally inside the table header, so the PR’s stated help-center fix is incomplete for tables. The fix should reuse the same href escaping/encoding helper in both the shared link.close path and the table-cell link branch.

[iamsivin]

@iamsivin can you take a look at this review comment:

Findings [P1] src/schema/markdown/serializer.js:225 still serializes table-cell links with raw mark.attrs.href. The PR fixes the shared link mark serializer, but serializeCellContent has its own link branch: [text](${mark.attrs.href})

So links inside article tables still emit invalid markdown when the href has spaces or parentheses. I verified this against PR head a5a2e3f: a table link with https://example.com/a path/foo(bar) serializes as:

| [inside](https://example.com/a path/foo(bar)) | plain |

Parsing that back splits the href at the space and leaves literal markdown in the cell. Chatwoot’s help-center renderer also renders it literally inside the table header, so the PR’s stated help-center fix is incomplete for tables. The fix should reuse the same href escaping/encoding helper in both the shared link.close path and the table-cell link branch.

@sony-mathew Handled