feat(post-form): U1 — shared create/edit form + published field + owner_username

One /post form now drives both create and edit (KTD1, Alt B): cache-on-save
toggles add-page-by-form's overwrite_mode per submit — 'edit' when the new hidden
edit_path field is filled (write back in place, stable URL), 'false' when empty
(fresh dated folder via slug_field). add-page-by-form stays stock (no fork);
the toggle lives in cache-on-save, which reads edit_path and mutates the /post
page header's pageconfig before add-page-by-form's onFormProcessed runs.

- post-form.md: overwrite_mode:false (create-safe fallback), hidden edit_path,
  authoritative published toggle (default on), removed the static
  pagefrontmatter.published so the field wins on every submit (KTD3).
- cache-on-save.php: editPathFromForm + setOverwriteMode helpers.
- site.yaml: owner_username (single source of truth for the KTD8 owner gate).

Verified against the 2.0.4 container: create writes a fresh dated folder with
published:true/false as a real boolean (V1, V2); edit writes in place with the
slug/URL unchanged; save-as-draft-on-create works.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H1FrCYNq6RXdGYbn5PFrhM

pages/02.post/post-form.md

@@ -6,13 +6,21 @@ access:
 
 # Parent (write target) is injected server-side from site.active_trip by the
 # cache-on-save plugin (onFormValidationProcessed) — no manual sync needed.
+#
+# overwrite_mode is toggled per submit by cache-on-save (KTD1, Alt B): edit when
+# the hidden edit_path field is filled (write back in place), false when empty
+# (create a fresh dated folder via slug_field). The static value here is the
+# create-safe fallback for if cache-on-save doesn't run — add-page-by-form stays
+# stock (no fork), so a static `edit` would break create (empty edit_path -> '.').
 pageconfig:
     slug_field: 'date,title'
     overwrite_mode: false
 
+# published is NOT a static pagefrontmatter default anymore — it is an
+# authoritative form field (below) so every submit (create AND edit) writes the
+# owner's chosen publish state. Only `template` stays static here.
 pagefrontmatter:
     template: entry
-    published: true
 
 form:
     name: new-entry
@@ -129,11 +137,36 @@ form:
                 'car': '🚗 Car'
                 'plane': '✈️ Plane'
 
+        # Hidden edit target. Empty on create (add-page-by-form falls through to
+        # slug_field and writes a fresh dated folder); on edit, post-form.js sets
+        # it to the entry's path so overwrite_mode:edit writes back in place.
+        -
+            name: edit_path
+            type: hidden
+            default: ''
+
         # Advanced fields — collapsed behind "More options" (see U5).
         # No hero_image field: journal entries render their hero from the first
         # uploaded photo (entry-journal.html.twig uses entry.media.images|first),
         # so an explicit hero filename was redundant. Stories still use hero_image
         # but they aren't posted through this form.
+        -
+            name: published
+            label: Published
+            # Authoritative publish state (replaces the removed static
+            # pagefrontmatter.published). Default ON so new entries publish; the
+            # owner flips it OFF to save/keep a draft, or to unpublish on edit.
+            # validate.type:bool keeps it a real boolean in frontmatter (not '0').
+            type: toggle
+            classes: advanced-field
+            highlight: 1
+            default: 1
+            options:
+                1: 'Yes'
+                0: 'No'
+            validate:
+                type: bool
+
         -
             name: force_connect
             label: Force connector line