M5: comment pop-up windows laid out as reply threads, fixed in size, scrolling and resizable (comment.popups)

The pop-up window now reads as the common readers' do:

- a one-line title bar with the comment's kind and author, its date and x,
  in the comment's colour; the body in a lighter tint, with fixed ink so it
  reads in either app theme;
- the comment's text, and each reply's, in a box typed in place;
- the replies as panels in thread order, each inside the panel of the reply
  it answers (/IRT), nesting at most eight deep;
- a Reply button under the comment and each reply, opening a box that
  answers that comment or reply (Enter starts a new line; Post or
  Ctrl/Cmd+Enter posts; Cancel closes it).

The window keeps the size of its pop-up's /Rect in points on screen as the
page zooms, instead of growing with the zoom; the text and replies scroll
inside it, with a scroll bar shown whenever there is more. Dragging its
lower right corner resizes it; the new size is saved as the pop-up's /Rect,
the window's upper left corner kept in place on screen (on a page turned a
quarter too), in one undo step. A /Rect with non-finite numbers gives the
least size.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyCfwzyRXj4VfQAVVdv

parity/acrobat-features.toml

@@ -4135,8 +4135,8 @@ milestone = "M5"
 status = "shipped"
 commands = []
 tools = ["comment_popup", "comment_list"]
-evidence = ["crates/ui-egui/tests/it/comments.rs::a_double_click_opens_a_notes_pop_up_which_drags_and_closes", "crates/annot/src/tests.rs::pop_ups_open_close_and_move_and_are_reported", "crates/automation/tests/it/automation.rs::comment_popups_are_opened_moved_and_listed", "crates/render/src/inspect/tests.rs::a_comments_pop_up_is_read_with_its_place_and_state"]
-notes = "double-click a comment to open its pop-up window on the page (its /Popup /Open and /Rect, so other viewers show it the same); author, date, the text typed in place and the replies; the title bar drags it, × closes it; each is an undo step. Not yet: Acrobat's pop-up options menu (reply, status, delete from the window), replying from the window, resizing the window, Preferences ▸ Commenting pop-up behaviours (open on roll-over, hide when the Comments list opens)"
+evidence = ["crates/ui-egui/tests/it/comments.rs::a_double_click_opens_a_notes_pop_up_which_drags_and_closes", "crates/ui-egui/tests/it/comments.rs::a_pop_up_threads_its_replies_and_takes_a_new_one", "crates/ui-egui/tests/it/comments.rs::a_long_thread_scrolls_inside_its_pop_up", "crates/ui-egui/tests/it/comments.rs::a_pop_ups_corner_resizes_it", "crates/ui-egui/tests/it/comments.rs::a_pop_up_resized_on_a_turned_page_stays_in_place", "crates/annot/src/tests.rs::pop_ups_open_close_and_move_and_are_reported", "crates/automation/tests/it/automation.rs::comment_popups_are_opened_moved_and_listed", "crates/render/src/inspect/tests.rs::a_comments_pop_up_is_read_with_its_place_and_state"]
+notes = "double-click a comment to open its pop-up window on the page (its /Popup /Open and /Rect, so other viewers show it the same), at the size its /Rect gives in points whatever the zoom; a title bar with the comment's kind, author and date; its text typed in place; its replies as panels, each inside the one it answers (/IRT), their text typed in place too; a Reply button under the comment and under each reply opens a box that answers it (Enter starts a new line, Post or Ctrl+Enter posts); the text and replies scroll inside the window; the title bar drags it, its lower right corner resizes it, × closes it; each is an undo step. Not yet: the window's options menu (status, mark, lock, delete from the window), collapsing a reply's answers, resizing from the other corners and sides, Preferences ▸ Commenting pop-up behaviours (open on roll-over, hide when the Comments list opens)"
 
 [[feature]]
 id = "comment.connector-lines"