M3: an attachment's row opens on a double-click and has a right-click menu (#3466) (#4513)

* M3: an attachment's row opens on a double-click and has a right-click menu (#3466)

In Acrobat, a right-click on an attachment offers Open and Save, and a
double-click opens it. PdfCraft's Attachments panel had only the buttons
at the end of each row.

Each row now senses clicks beneath its buttons (`UiBuilder::sense`, which
egui registers under the row's children, so the buttons keep their own
clicks):
- A double-click opens a PDF in a new tab, as the Open button does, and
  saves any other file, since PdfCraft opens only PDFs.
- A right-click offers the row's own actions with the buttons' labels:
  Open in a new tab (PDFs), Save attachment… and Delete attachment (the
  document's own attachments, when it may be modified).

The name and details labels are no longer selectable, so a click on them
reaches the row.

* M3: a right-click on an attachment row's button opens the row's menu too (#3466)

CodeRabbit on #4513: the menu hung on the row's response only, so a
right-click on its Save, Open or Delete button opened nothing. The menu
now answers the union of the row and its buttons (one menu, the row's id).
Regression test right-clicks a button (fails without the fix).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LymhVaGZCWwB9HNEbLzeMM

---------

Co-authored-by: Claude <noreply@anthropic.com>

parity/acrobat-features.toml

@@ -1322,8 +1322,8 @@ milestone = "M3"
 status = "shipped"
 commands = []
 tools = ["doc_info"]
-evidence = ["crates/render/src/inspect.rs::attachments_of_both_kinds_are_listed_and_extracted"]
-notes = ""
+evidence = ["crates/render/src/inspect.rs::attachments_of_both_kinds_are_listed_and_extracted", "crates/ui-egui/tests/it/attachment_row.rs::the_right_click_menu_opens_saves_and_deletes", "crates/ui-egui/tests/it/attachment_row.rs::double_clicking_a_pdf_attachment_opens_it_in_a_new_tab"]
+notes = "Each row has Save, Open in a new tab (PDFs) and Delete (the document's own attachments) buttons, the same items on a right-click, and a double-click that opens a PDF in a new tab or saves any other file (#3466). Not yet: Acrobat's Search attachments, and opening a non-PDF attachment in another program (it is saved instead)."
 
 [[feature]]
 id = "view.layers-panel"