M7: offer to lock a signature right after it's placed, and keep the switch in the panel (#2149)

benandez's review suggestion on #2348. Right after Fill & Sign places a
signature or initials, a notice says "Signature added. Others can move it
until it's locked." with Lock now, which flattens the marks into the page
(undoable) without saving; the save that follows then has nothing to ask
about. The placed-signature mark is kept, so undoing the lock brings back the
notice and the save-time question, which stays as the fallback. Dismiss hides
the notice until the next signature. No notice on a digitally signed document
or when saves lock anyway. The "Lock into the page when saving" switch is
now once, in the panel's Sign yourself section, no longer in the Sign menu
over the page. The three new strings are in all 22 catalogues (AI-assisted,
not reviewed by native speakers).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

parity/acrobat-features.toml

@@ -5441,8 +5441,8 @@ milestone = "M5"
 status = "shipped"
 commands = ["comment.flatten"]
 tools = ["doc_save", "doc_flatten"]
-evidence = ["crates/edit/src/tests.rs::fill_sign_flatten_bakes_marks_keeps_other_comments_and_does_not_reuse_pcfl0", "crates/engine/src/tests.rs::flattening_fill_and_sign_keeps_other_comments_fields_and_undoes", "crates/engine/src/tests.rs::flattening_fill_and_sign_is_refused_without_permission_to_change", "crates/automation/tests/it/automation.rs::saving_with_flatten_fill_sign_bakes_marks_and_leaves_other_comments", "crates/ui-egui/tests/it/fill_sign.rs::saving_flattens_fill_and_sign_only_when_the_preference_is_on", "crates/ui-egui/tests/it/fill_sign.rs::the_first_save_after_placing_a_signature_asks_to_lock_it", "crates/ui-egui/tests/it/fill_sign.rs::cancelling_the_lock_question_saves_nothing", "crates/ui-egui/tests/it/fill_sign.rs::a_lock_that_fails_keeps_the_question", "crates/ui-egui/tests/it/fill_sign.rs::the_lock_question_is_skipped_or_kept_where_it_must_be"]
-notes = "Preferences ▸ Fill & Sign, and doc_save flatten_fill_sign, bake text, marks and signatures into the page. The option defaults off, so a normal save leaves them editable; the first save after a signature or initials is placed asks whether to lock it into the page (Lock and save / Keep editable, with Don't ask again), and the Sign menu carries the same switch (#2149). Other comments and form fields stay. Flatten comments still flattens every comment."
+evidence = ["crates/edit/src/tests.rs::fill_sign_flatten_bakes_marks_keeps_other_comments_and_does_not_reuse_pcfl0", "crates/engine/src/tests.rs::flattening_fill_and_sign_keeps_other_comments_fields_and_undoes", "crates/engine/src/tests.rs::flattening_fill_and_sign_is_refused_without_permission_to_change", "crates/automation/tests/it/automation.rs::saving_with_flatten_fill_sign_bakes_marks_and_leaves_other_comments", "crates/ui-egui/tests/it/fill_sign.rs::saving_flattens_fill_and_sign_only_when_the_preference_is_on", "crates/ui-egui/tests/it/fill_sign.rs::placing_a_signature_offers_to_lock_it_now", "crates/ui-egui/tests/it/fill_sign.rs::the_first_save_after_placing_a_signature_asks_to_lock_it", "crates/ui-egui/tests/it/fill_sign.rs::cancelling_the_lock_question_saves_nothing", "crates/ui-egui/tests/it/fill_sign.rs::a_lock_that_fails_keeps_the_question", "crates/ui-egui/tests/it/fill_sign.rs::the_lock_question_is_skipped_or_kept_where_it_must_be"]
+notes = "Preferences ▸ Fill & Sign, and doc_save flatten_fill_sign, bake text, marks and signatures into the page. The option defaults off, so a normal save leaves them editable; right after a signature or initials is placed, a notice offers Lock now (undoable, no save), and the first save after one is placed asks whether to lock it into the page (Lock and save / Keep editable, with Don't ask again); the Fill & Sign panel's Sign yourself section carries the same switch (#2149). Not on a digitally signed document. Other comments and form fields stay. Flatten comments still flattens every comment."
 
 [[feature]]
 id = "form.autofill-profile"