Replace render_turbo_stream cancel handlers with form#cancel Stimulus action

Add cancel() method to form_controller that handles all close cases:
- tabular forms (<tr>): removes inner form, re-enables link, shows hidden row
- measurements create form: removes self, enables trigger link, shows no-items

Data attributes already present on controller elements (data-form, data-link,
data-hidden-row) drive the behaviour. Two extra attributes on the create form
(data-cancel-enable, data-cancel-show) cover the non-tabular case.

Delete now-unused _form_close and _edit_form_close partial templates.

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

app/javascript/controllers/form_controller.js

@@ -22,4 +22,30 @@ export default class extends Controller {
       event.preventDefault()
     }
   }
+
+  cancel(event) {
+    event.preventDefault()
+    const el = this.element
+
+    // Move focus to next open form if this one had focus
+    const focused = document.activeElement
+    if (!focused || focused === document.body || el.contains(focused)) {
+      const next = el.parentElement?.querySelector(`#${el.id} ~ tr:has([autofocus])`)
+        ?? el.parentElement?.querySelector("tr:has([autofocus])")
+      next?.querySelector("[autofocus]")?.focus()
+    }
+
+    // Remove associated inner form element (tabular: <tr> wraps a separate <form>)
+    document.getElementById(el.dataset.form)?.remove()
+
+    // Re-enable trigger link
+    const enableId = el.dataset.link ?? el.dataset.cancelEnable
+    if (enableId) Turbo.StreamElement.prototype.enableElement(document.getElementById(enableId))
+
+    // Show hidden row (tabular forms) or no-items placeholder (create form)
+    document.getElementById(el.dataset.hiddenRow)?.removeAttribute("style")
+    document.getElementById(el.dataset.cancelShow)?.style.removeProperty("display")
+
+    el.remove()
+  }
 }