Keep what was typed when a target or webhook edit is refused (closes #381)

A refused save on the target edit page answered with a bare text page, losing the form and everything typed, and the webhook edit page came back with the stored values instead of the submitted ones. A refused target edit now shows the edit form again with the reason above it and every value submitted, with the same status codes as before; a refused webhook edit keeps the submitted name, description and retention. Target edits use the same validation as new targets, with no second copy; an encoding or database failure stays a logged 500. The browser test covers a refused save on both pages, and its main function is now a plain list of checks.

Model: opus-5-5

README.md

@@ -1350,23 +1350,25 @@ markup. The CSP build runs no expressions, so every Alpine directive in
 `static/js/app.js`: `x-data="collapsible"` and `@click="toggle"`, never
 `x-data="{ open: false }"` or `@click="open = !open"`.
 
-A browser test in `internal/server` loads the webhook page and the event log
-under the real policy and checks that: the add entrypoint form stays hidden
-until Add is clicked; for every target type, the targets section's Add shows
-only a choice of type with Next and Cancel, Next shows only that type's fields
-(no url field for `database` or `log`), Cancel at either step closes the form,
-and saving adds the target; a refused target comes back with its form open, the
-values entered and the reason, and after Cancel the next Add starts with an
-empty form and no reason; the Copy button beside an entrypoint URL reads
-"Copied" once clicked; an entrypoint's Edit button shows its edit form in place
-of its description and hides until the form closes, Cancel hides the form and
-drops what was typed, as does leaving the page and going back to it, and Save
-changes the description; of the recent events on the webhook page only the
-newest starts expanded, each expands and collapses, and Open leads to the
-event's own page; an event in the event log expands and collapses, and so do a
-delivery's attempts inside it; and at phone width the menu button opens and
-closes the mobile menu. It also fails if the browser reports a console warning
-or error, an uncaught exception, or anything the policy refused. `make check`
+A browser test in `internal/server` loads the webhook page, its edit pages and
+the event log under the real policy and checks that: the add entrypoint form
+stays hidden until Add is clicked; for every target type, the targets section's
+Add shows only a choice of type with Next and Cancel, Next shows only that
+type's fields (no url field for `database` or `log`), Cancel at either step
+closes the form, and saving adds the target; a refused target comes back with
+its form open, the values entered and the reason, and after Cancel the next Add
+starts with an empty form and no reason; a refused save on the target edit page
+and on the webhook edit page comes back with the reason and every value
+entered; the Copy button beside an entrypoint URL reads "Copied" once clicked;
+an entrypoint's Edit button shows its edit form in place of its description and
+hides until the form closes, Cancel hides the form and drops what was typed, as
+does leaving the page and going back to it, and Save changes the description;
+of the recent events on the webhook page only the newest starts expanded, each
+expands and collapses, and Open leads to the event's own page; an event in the
+event log expands and collapses, and so do a delivery's attempts inside it; and
+at phone width the menu button opens and closes the mobile menu. It also fails
+if the browser reports a console warning or error, an uncaught exception, or
+anything the policy refused. `make check`
 and the image build lint it but do not run it, and `make test` leaves it out
 (its file is built only with the `browser` build tag). Run it with
 `make test-browser` after changing `templates/` or `static/js/`: that builds