feat(editor): preserve arbitrary font sizes and families in content

[dagyu]

Problem — custom HTML signatures don't work

Setting a custom HTML signature (a branded block with specific fonts and
sizes — e.g. a 13pt name, 11pt role/phone, 9pt address, a logo and links) is a
common, reasonable requirement. Today it's effectively impossible to do
faithfully through Mail: the signature is stored correctly, looks correct in
account settings, but loses its typography the moment it passes through the
composer, and reaches recipients with the wrong size and font.

Concretely, given a signature span like:

<span style="color:#3c3c3b;font-family:Arial,Helvetica,sans-serif;font-size:13pt">…</span>

the recipient receives:

<span style="color:#3c3c3b">…</span> ← font-size and font-family gone.

color survives; font-size and font-family are dropped. There is no way to
work around it from the signature HTML — the loss happens inside the editor.

Root cause

The composer's CKEditor FontSize / FontFamily plugins run with their
default presets and supportAllValues disabled. When signature/pasted HTML is
inserted into the editor, any font-size or font-family that isn't one of
the built-in presets is stripped during the model round-trip. (color is kept
because FontColor accepts all values by default — which is exactly the
behaviour size/family should have too.)

Fix

Enable supportAllValues: true on both Font plugins so inline font-size and
font-family survive:

fontSize: {
    options: [9, 10, 11, 12, 13, 14, 16, 18, 24, 'default'],
    supportAllValues: true,
},
fontFamily: {
    supportAllValues: true,
},

[ChristophWurst]

Thanks for the changes

How can this be tested? The signature editor doesn't allow arbitrary font sizes either, does it?

It would be best if you could provide before and after screenshots that demo the change in addition to textual steps to reproduce.

Please point your agents to AGENTS.md to fix the commit footer.

[dagyu]

@ChristophWurst I update the commit footer as written in AGENTS.md.

Following videos show exactly the bug that I had, without the patch it is impossible for me to customize the font size cause the editor doesn't preserve the values. First video is current main version, second one is the patched version.

OLD.mov

NEW.mov

[GretaD]

tested and it works, thanks a lot

[dagyu]

Can you tell me please if you are planning to put this in the next release? Because I need it so if you can't I will install patched version