contact messages: label is the enable switch; single-line settings row

Data.contact_enabled is gone: an empty contact label disables messaging
(no buttons, no visitor icon, sends rejected). The settings row is one
line — flag selector, label, email, subject as small boxes with tooltip
instructions — and saves re-render the page in place so button/dialog
strings update without a reload; the open dialog also re-reads its
strings on page swaps. The built-in Contact us default survives only as
the inert preview placeholder.

docs/messages.md

@@ -12,8 +12,8 @@ existing WebSockets; there is no REST polling anywhere.
   thread store ops, wire payloads, both socket protocols, the admin unread
   count and the `/_contact/files` upload route.
 - `pagerite/data.py` — `Data.contact` (`ContactThread`/`ContactMessage`)
-  and the site settings (`contact_enabled`, `contact_label`,
-  `contact_email`, `contact_subject`).
+  and the site settings (`contact_label` — which doubles as the on/off
+  switch — `contact_email`, `contact_subject`).
 - `pagerite/tracking.py` — the sockets the protocol rides (see below).
 - `pagerite/api.py` — `/_api/settings` carries `contact_unread` (the admin
   icon badge seed — the probe runs on every page load, no polling) and the
@@ -36,40 +36,44 @@ A lone `{contact: Label}` line in article Markdown (the block-directive
 machinery of `markdown.py`) renders
 `<button class="contact-trigger">Label</button>`. An empty label falls
 back to the configured site label (`Data.contact_label`, localized —
-below), ultimately the built-in "Contact us". `pagerite.js`
+below; "Contact us" appears only as the inert preview's placeholder when
+nothing is configured). `pagerite.js`
 click-delegates these buttons and lazy-loads
 the contact bundle; the editor preview renders the same button inert, and
 description/card mining resolves the tag to nothing. A per-button label
 lives in the chunk, so translated pages localize it like any other text.
 Feeds render the tag as its literal source (no directive context). When
-messaging is disabled the tag renders nothing at all.
+messaging is disabled (no site label configured) the tag renders nothing
+at all.
 
 ## Site settings and localization
 
-The site editor's messaging block holds the feature's configuration
-(`/_api/settings`): `contact_enabled` (off = no trigger buttons, no
-visitor corner icon, sends rejected; admins keep the inbox for existing
-threads), `contact_email` (a mailto link in the visitor dialog, its
-subject prefilled) and the `contact_label`/`contact_subject` strings
-(the label doubles as the dialog's title and the buttons' default; the
-subject defaults to the label).
+The site editor's messaging row holds the feature's configuration
+(`/_api/settings`): `contact_label` — the {contact:} buttons' label and
+the visitor dialog's title, doubling as the on/off switch (empty = no
+trigger buttons, no visitor corner icon, sends rejected; admins keep the
+inbox for existing threads) — `contact_email` (a mailto link in the
+visitor dialog, its subject prefilled) and `contact_subject` (defaults
+to the label). Saves re-render the page in place, so button and dialog
+strings update without a reload.
 
 The two strings localize like titles: translations live in the
 chunk-keyed `Data.trans` store (`i18n.site_string` looks them up at
-render time — the *effective* label, so the built-in default localizes
-too) and the translator service picks them up automatically
+render time) and the translator service picks them up automatically
 (`pending_items` emits them as title-kind fragments; nav-mode jobs carry
 them as extra top-level list items). Manual overrides are edited in the
-same messaging block: its language selector switches the label/subject
-fields to a translation, saved via `PUT /_api/settings?lang=` into the
+same messaging row: the flag selector (the article editor's LangSelect)
+switches the label/subject fields to a translation, saved via
+`PUT /_api/settings?lang=` into the
 same store (`i18n.set_string_translation`; empty or the original's text
 drops the override). The localized strings reach the client through the
 page's asset config (`pagerite:contact-label` / `-subject`, absent
 entirely when disabled — pagerite.js reads that as "visitors get no
-icon"); `contact-main.js` re-reads them on every open, so a language
-switch is reflected immediately. The email address itself is never in
-the config: it is revealed over the messaging socket only after the
-proof of work is solved.
+icon"); `contact-main.js` re-reads them on every open and on page swaps,
+so a language switch or a settings save is reflected immediately. The
+email address itself is never in the config: it is revealed over the
+messaging socket only after the proof of work is solved (and only when
+configured).
 
 ## Visitor side