**Steps to reproduce:**
1. Go to Accounting > Customers > create a company with child contact (invoice) (both having name and email).
2. Create an invoice with the child contact as customer and confirm it.
3. Go to the child contact and open the Customer Statement smart button.
4. Download the PDF → data is shown correctly.
5. Send the statement → the attachment in the sent mail is empty.

**Issue:**
- When sending customer statements via email from a child contact, the generated
  PDF attachment contains no data, showing empty amounts and transactions.
- Additionally, the "Customer Statement" button was still visible even when
  the total due was zero.

**Cause:**
- The button visibility condition checks for `total_due == 0.0 and not has_moves`,
  which didn’t properly cover all use cases.

**Solution:**
- Update button visibility condition to: `invisible="not has_moves or total_due == 0"`
  ensuring it is hidden when there are no moves or the total due is zero.

**opw-5009182**

Forward-Port-Of: odoo/enterprise#93162

### Issue 1:

Summary:
When a user adds a comment inside a baseContainer element, the comment
beacons created during the comment insertion can be discarded during
the document normalization step.

How to reproduce:
- Open an article in Knowledge.
- Select text and change the block style from "Paragraph" to "Normal"
  using the powerbox.
- Add a comment on the selected text using the powerbox.
- Write a message in the comment thread.
- Save and reload the article.

Issue:
- The comment beacons disappears from the editor and the user can't see it
  anymore.

Resolution:
When the editor is initialized, `div` are not yet categorized as
paragraph related elements. The `comments_plugin` logic to identify valid
positions for comments beacons should take that into account and allow elements
which are candidates to be a paragraph related element.

### Issue 2:

Summary:
There was an issue where comments were not displayed when switching from a
locked article to another (read-only).

How to reproduce:
- Create two articles and add a comment on each.
- Lock both articles (so that they are effectively read-only).
- Switch from one article to the other.

Issue:
- Comments are not displayed to the user.

Resolution:
When switching between read-only articles, `KnowledgeHtmlViewer` is
not fully reloaded and continues using the same `CommentBeaconManager`
instance for the newly opened article. As a result, comment beacons
are not displayed when switching article. The simplest solution to this issue is
to re-instantiate a new `CommentBeaconManager` whenever the HTML value changes
to ensure comments are correctly displayed.

### Issue 3:

There is an issue in the logic of `computeVerticalDimensions` to display
comments. If the `top` value of a thread in the article is `0`, it will be
filtered out and not displayed because `top` was used as a boolean value.
Instead, it should properly consider `top` as a finite number to display the
comment or not.

Note:
This issue is not easily reproducible because there are few configuration where
a comment would have a top value equal to 0.

### Issue 4:

There is a crash when inserting a knowledge comment in a `/code` block:
In this previous [task], insertion in `pre` elements was filtered to prevent
non-phrasing content from being inserted (as it is invalid per the html
specification). To prevent a crash, knowledge comments will be disabled in
`<pre>` elements, as they rely on `anchor` elements for the comment position in
the article body.

[task]: 216e9eb

task-4984152

Forward-Port-Of: odoo/enterprise#91408