Extract DateTime picker to static JS file

Moves ~50 lines of inline JavaScript from event_datetime_field() to a
static file. The component now uses data attributes for element binding
and global functions (toggleDatetimePicker, updateDatetimeTs) from the
static JS file.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/animaltrack/static/v1/datetime-picker.js

@@ -0,0 +1,53 @@
+/**
+ * Datetime Picker Component
+ *
+ * Provides toggle and conversion functionality for backdating events.
+ * Uses data attributes to identify related elements.
+ *
+ * Expected HTML structure:
+ * - Toggle element: data-datetime-toggle="<field_id>"
+ * - Picker container: data-datetime-picker="<field_id>"
+ * - Input element: data-datetime-input="<field_id>"
+ * - Hidden ts_utc field: data-datetime-ts="<field_id>"
+ */
+
+/**
+ * Toggle the datetime picker visibility.
+ * @param {string} fieldId - The unique field ID prefix.
+ */
+function toggleDatetimePicker(fieldId) {
+    var picker = document.querySelector('[data-datetime-picker="' + fieldId + '"]');
+    var input = document.querySelector('[data-datetime-input="' + fieldId + '"]');
+    var tsField = document.querySelector('[data-datetime-ts="' + fieldId + '"]');
+    var toggle = document.querySelector('[data-datetime-toggle="' + fieldId + '"]');
+
+    if (!picker || !toggle) return;
+
+    if (picker.style.display === 'none') {
+        picker.style.display = 'block';
+        toggle.textContent = 'Use current time';
+    } else {
+        picker.style.display = 'none';
+        toggle.textContent = 'Set custom date';
+        if (input) input.value = '';
+        if (tsField) tsField.value = '0';
+    }
+}
+
+/**
+ * Update the hidden ts_utc field when datetime input changes.
+ * @param {string} fieldId - The unique field ID prefix.
+ */
+function updateDatetimeTs(fieldId) {
+    var input = document.querySelector('[data-datetime-input="' + fieldId + '"]');
+    var tsField = document.querySelector('[data-datetime-ts="' + fieldId + '"]');
+
+    if (!tsField) return;
+
+    if (input && input.value) {
+        var date = new Date(input.value);
+        tsField.value = date.getTime().toString();
+    } else {
+        tsField.value = '0';
+    }
+}

src/animaltrack/web/templates/actions.py

@@ -4,7 +4,7 @@
 from collections.abc import Callable
 from typing import Any
 
-from fasthtml.common import H2, H3, Div, Form, Hidden, Input, Option, P, Select, Span
+from fasthtml.common import H2, H3, Div, Form, Hidden, Input, Option, P, Script, Select, Span
 from monsterui.all import (
     Alert,
     AlertT,
@@ -142,43 +142,14 @@ def event_datetime_field(
     Returns:
         Div containing the datetime picker with toggle functionality.
     """
-    picker_id = f"{field_id}_picker"
-    input_id = f"{field_id}_input"
-    ts_utc_id = f"{field_id}_ts_utc"
-
     # If initial value is set, start with picker expanded
     has_initial = bool(initial_value)
     picker_style = "display: block;" if has_initial else "display: none;"
     toggle_text = "Use current time" if has_initial else "Set custom date"
 
-    # Inline JavaScript for toggle click handler
-    toggle_onclick = f"""
-        var picker = document.getElementById('{picker_id}');
-        var input = document.getElementById('{input_id}');
-        var tsField = document.getElementById('{ts_utc_id}');
-        if (picker.style.display === 'none') {{
-            picker.style.display = 'block';
-            this.textContent = 'Use current time';
-        }} else {{
-            picker.style.display = 'none';
-            this.textContent = 'Set custom date';
-            input.value = '';
-            if (tsField) tsField.value = '0';
-        }}
-    """
-
-    # Inline JavaScript for input change handler
-    input_onchange = f"""
-        var tsField = document.getElementById('{ts_utc_id}');
-        if (tsField && this.value) {{
-            var date = new Date(this.value);
-            tsField.value = date.getTime().toString();
-        }} else if (tsField) {{
-            tsField.value = '0';
-        }}
-    """
-
     return Div(
+        # Load static JS for datetime picker functionality
+        Script(src="/static/v1/datetime-picker.js"),
         FormLabel("Event Time"),
         Div(
             P(
@@ -187,29 +158,30 @@ def event_datetime_field(
                 Span(
                     toggle_text,
                     cls="text-blue-400 hover:text-blue-300 cursor-pointer underline",
-                    hx_on_click=toggle_onclick,
+                    data_datetime_toggle=field_id,
+                    hx_on_click=f"toggleDatetimePicker('{field_id}')",
                 ),
                 cls="text-sm",
             ),
             Div(
                 Input(
-                    id=input_id,
                     name=f"{field_id}_value",
                     type="datetime-local",
                     value=initial_value,
                     cls="uk-input w-full mt-2",
-                    hx_on_change=input_onchange,
+                    data_datetime_input=field_id,
+                    hx_on_change=f"updateDatetimeTs('{field_id}')",
                 ),
                 P(
                     "Select date/time for this event (leave empty for current time)",
                     cls="text-xs text-stone-500 mt-1",
                 ),
-                id=picker_id,
+                data_datetime_picker=field_id,
                 style=picker_style,
             ),
             cls="mt-1",
         ),
-        Hidden(id=ts_utc_id, name="ts_utc", value=initial_ts),
+        Hidden(name="ts_utc", value=initial_ts, data_datetime_ts=field_id),
         cls="space-y-1",
     )