feat: floating composer

[aerodeval]

Replaces the ticket page's EmailEditor / CommentTextEditor with the @framework/ui EmailComposer / CommentComposer hosted in a frappe-ui/experimental FloatingWindow. One rewritten file, both old editors deleted, net −522 lines.

Depends on frappe/frappe#40280 (@framework/ui composers). Draft until that lands.

What changes

• The reply area is a minimized pill by default. Clicking it opens the composer docked at the bottom of the timeline; it can be popped out into a floating window, dragged, and resized from any edge or corner.
• Email / Comment are tabs inside the window header instead of two separate editors.
• Drag the docked header — or either top corner — to set the composer height. It persists per browser and is restored on reopen and reload. Dragging 60px below the floor collapses back to the pill.
• Drafts, mentions, saved replies, attachments, signatures and the existing localStorage draft keys all behave as before.

Before / after

	Before	After
Reply area	Always-expanded editor pinned under the timeline, fixed height	Minimized pill; composer opens over the timeline, height is drag-set and remembered
Channels	Separate email box and comment box, toggled from outside	One window, Email / Comment tabs in its header
Window	Fixed in the page	Docked or floating — draggable, resizable from every edge and corner
Empty pill label	"Add a comment"	"Send a reply" (clicking it opens the email reply)

Screenshots

Before	After
Reply bar	Minimized pill
Email editor	Docked composer
	Floating window

Notes

• EmailComposer header rows now share a grid so the label column is only as wide as the widest label rendered — previously a hardcoded 52px sized for a "Subject" row helpdesk never shows, which left a visible gap between "To" and its recipients. That part lives in the frappe PR.
• Not yet covered: a ticket whose thread contains a very large table can wedge the composer on open — under investigation, unrelated to the window itself.

Demo:

Screen.Recording.2026-08-05.at.4.03.23.AM.mov

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.80%. Comparing base (c3ae467) to head (6542db6).
⚠️ Report is 5 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3674      +/-   ##
===========================================
+ Coverage    73.76%   73.80%   +0.03%     
===========================================
  Files          148      148              
  Lines        10841    10845       +4     
===========================================
+ Hits          7997     8004       +7     
+ Misses        2844     2841       -3     

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