fix: rewire add-page-by-form so posts actually get created

Two root-cause bugs:
1. Wrong action name: 'add-page-by-form' is not handled by the plugin;
   the plugin only matches 'addpage' or 'add_page'. Using the wrong name
   meant the action silently no-oped while 'message' still fired, showing
   'Entry posted successfully!' for a post that was never written.
2. Config in wrong place: parent/slug/template must be in 'pageconfig' and
   'pagefrontmatter' frontmatter blocks on the form page — the plugin reads
   from page->header(), not from the process block params.

Fix: move config to pageconfig/pagefrontmatter, change action to 'add_page'.
Slug is built from date+title fields (e.g. 2026-06-18-1430-my-title).
Photos destination changed to '@self' so the plugin copies from flash to
the new entry folder correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pages/02.post/post-form.md

@@ -3,7 +3,16 @@ title: 'New Entry'
 template: post-form
 access:
     site.login: true
-login_redirect_here: true
+
+pageconfig:
+    parent: '/tracker'
+    slug_field: 'date,title'
+    overwrite_mode: false
+
+pagefrontmatter:
+    template: entry
+    published: true
+
 form:
     name: new-entry
     action: /post
@@ -39,7 +48,7 @@ form:
             label: Photos (max 4)
             type: file
             multiple: true
-            destination: 'user://pages/01.tracker'
+            destination: '@self'
             limit: 4
             accept:
                 - 'image/*'
@@ -84,19 +93,7 @@ form:
 
     process:
         -
-            add-page-by-form:
-                parent: '/tracker'
-                slug: "{{ form.value.date|date('Y-m-d-Hi') }}-{{ form.value.title|lower|regex_replace('/[^a-z0-9]+/', '-')|trim('-') }}"
-                template: 'entry'
-                frontmatter:
-                    title: '{{ form.value.title }}'
-                    date: '{{ form.value.date }}'
-                    lat: '{{ form.value.lat }}'
-                    lng: '{{ form.value.lng }}'
-                    location_city: '{{ form.value.location_city }}'
-                    location_country: '{{ form.value.location_country }}'
-                    weather_temp_c: '{{ form.value.weather_temp_c }}'
-                    weather_desc: '{{ form.value.weather_desc }}'
+            add_page: true
         -
             message: 'Entry posted successfully!'
         -