sky form TZ: render-readonly + drop #id_nf_tz_hint; placeholder absorbs the auto-detected hint copy — TDD

A user-typed TZ override fed through schedulePreview's `if (tz) params.set('tz', tz)` path made PySwiss compute the chart against a TZ that didn't match the lat/lon, so a partial edit (e.g. "America/New_Yo|") returned HTTP 400. Mirror the lat/lon convention: tz field gets readonly + tabindex:-1 across all three sky contexts (Dashsky sky.html, in-room PICK SKY _sky_overlay.html, My Sky applet _applet-my-sky.html). Auto-population still works because the JS writes via .value rather than via user input. The <small id="id_nf_tz_hint"> "Auto-detected from coordinates." line is removed; that copy now lives on the <input>'s placeholder so an empty TZ field self-explains. JS purges every tzHint reference (const declaration + 4 .textContent writes per file × 3 files).

SkyViewTest.test_tz_input_is_readonly_and_carries_auto_detect_placeholder pins the rendered Dashsky markup: id_nf_tz carries `readonly`, the placeholder is "auto-detected from coordinates", and `id="id_nf_tz_hint"` no longer appears anywhere. Existing MySkyTimezoneRefreshTest still passes — it asserts the field auto-fills via JS, which still works on a readonly input.

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Sonnet 4.6 <noreply@anthropic.com>

src/apps/dashboard/tests/integrated/test_sky_views.py

@@ -37,6 +37,22 @@ class SkyViewTest(TestCase):
         self.assertContains(response, reverse("sky_preview"))
         self.assertContains(response, reverse("sky_save"))
 
+    def test_tz_input_is_readonly_and_carries_auto_detect_placeholder(self):
+        """Manual TZ edits throw the schedulePreview / PySwiss fetch off (the
+        backend gets a stale TZ for the new lat/lon), so the field is render-
+        readonly like lat/lon — auto-fills from preview, never from a typed
+        override. The old <small id="id_nf_tz_hint"> is gone; its copy lives
+        in the placeholder so an empty field is self-explanatory."""
+        response = self.client.get(reverse("sky"))
+        self.assertContains(response, 'id="id_nf_tz"')
+        # readonly + tabindex:-1 mirrors the lat/lon pattern.
+        self.assertRegex(
+            response.content.decode(),
+            r'id="id_nf_tz"[^>]*\breadonly\b',
+        )
+        self.assertContains(response, 'placeholder="auto-detected from coordinates"')
+        self.assertNotContains(response, 'id="id_nf_tz_hint"')
+
 
 class SkyPreviewTest(TestCase):
     def setUp(self):