Add optional dates to the Training issue template

Same gap as Events had: the Training detail card supports a "Date(s)"
row (date + date_end) for a specific dated delivery — a workshop
cohort, a bootcamp — but the issue template had no way to supply it.
Both fields are optional and explicitly say to leave them blank for
self-paced or ongoing courses, matching the card's own require_end
behavior (the row only shows once both are set).

Checked the remaining templates (Books, Community, Press) against
their current cards while at it — all three already match, no changes
needed there.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: Mazizova

.github/ISSUE_TEMPLATE/resource-training.yml

@@ -29,6 +29,18 @@ body:
     attributes:
       label: "Author or organization"
       placeholder: "e.g. Kedar Vaijanapurkar"
+  - type: input
+    id: date
+    attributes:
+      label: "Start date (optional)"
+      description: "Only for a specific dated delivery — a workshop cohort, a bootcamp. Leave blank for self-paced or ongoing courses."
+      placeholder: "e.g. 2027-06-15"
+  - type: input
+    id: date_end
+    attributes:
+      label: "End date (optional)"
+      description: "Only if you set a start date above."
+      placeholder: "e.g. 2027-06-17"
   - type: dropdown
     id: subcategory
     attributes: