contact messages: keep password managers off the messaging settings boxes

Renaming subject->topic wasn't enough (both email and topic still got
credential autofill offers, and autocomplete=off is ignored). The three
messaging inputs are now readonly until the first pointerdown/focus —
managers skip readonly fields at scan time — backed up by the vendor
ignore attributes (1Password/LastPass/Bitwarden).

frontend/src/SiteEditor.vue

@@ -75,6 +75,11 @@ const contactLabel = ref('')
 const contactSubject = ref('')
 const contactLabelOrig = ref('')
 const contactSubjectOrig = ref('')
+// Password managers offer credential autofill on these boxes no matter
+// the autocomplete setting; readonly until the first interaction keeps
+// them off (the vendors' ignore attributes on the inputs back it up).
+const pmGuard = ref(true)
+const pmUnlock = () => { pmGuard.value = false }
 const lang = editorLang // '' = the original strings (the primary language)
 const primaryLang = ref('en')
 const translateLangs = ref([])
@@ -775,6 +780,12 @@ onUnmounted(() => {
           class="text-input"
           :placeholder="translating ? contactLabelOrig : 'Contact us'"
           title="Messaging: the {contact:} button label and visitor dialog title — empty disables messaging"
+          :readonly="pmGuard"
+          data-1p-ignore
+          data-lpignore="true"
+          data-bwignore
+          @pointerdown="pmUnlock"
+          @focus="pmUnlock"
           @input="onContactInput"
         />
         <input
@@ -783,6 +794,12 @@ onUnmounted(() => {
           placeholder="email"
           title="Contact email — a mailto link in the visitor dialog, revealed only after the proof of work is solved (empty = no link)"
           :disabled="!!translating"
+          :readonly="pmGuard"
+          data-1p-ignore
+          data-lpignore="true"
+          data-bwignore
+          @pointerdown="pmUnlock"
+          @focus="pmUnlock"
           @input="debounce('contact-email', () => saveSettings())"
         />
         <input
@@ -790,6 +807,12 @@ onUnmounted(() => {
           class="text-input"
           :placeholder="translating ? contactSubjectOrig : 'topic'"
           title="Topic for the mailto link (empty = the label)"
+          :readonly="pmGuard"
+          data-1p-ignore
+          data-lpignore="true"
+          data-bwignore
+          @pointerdown="pmUnlock"
+          @focus="pmUnlock"
           @input="onContactInput"
         />
       </div>
@@ -927,9 +950,10 @@ onUnmounted(() => {
 
 /* The messaging block: one line — the article editor's flag selector,
    then small text boxes (label = the enable switch, email, topic). The
-   mailto subject is labeled "topic" in the UI: password managers
-   mistake an input named "subject" for a credential field and offer
-   autofill no matter the autocomplete setting. */
+   boxes are readonly until first interaction (+ vendor ignore
+   attributes, and the mailto subject is labeled "topic"): password
+   managers offer credential autofill on them no matter the
+   autocomplete setting. */
 .msg-head {
   flex-wrap: wrap;
 }