chore: rework issue and discussion templates around scope policy

Issue forms: trim prerequisite checkboxes to the two that matter, make the
yt-dlp test field explicitly conditional (UI bugs write "UI bug"), lead the
feature form with the scope line and the already-decided list, and retire
the question template in favor of Discussions Q&A.

Discussion forms: rename q-and-a.yml to q-a.yml so it matches the actual
category slug (it never applied), add ideas.yml for the category where
feature requests actually land, drop configuration-help.yml (no matching
category) and the inert config.yml (blank_discussions_enabled is not a
GitHub feature), and remove checkboxes from low-stakes discussion forms.

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

.github/DISCUSSION_TEMPLATE/general.yml

@@ -1,30 +1,13 @@
-name: 💬 General Discussion
-description: Start a general discussion about MeTube
-title: "[Discussion]: "
-labels: ["discussion"]
-assignees: []
-
 body:
-  - type: checkboxes
-    id: prerequisites
-    attributes:
-      label: Prerequisites
-      description: Please confirm you have completed these steps before starting a discussion
-      options:
-        - label: I have searched existing discussions to ensure this topic hasn't been discussed before
-          required: true
-        - label: I have read the [README](https://github.com/alexta69/metube#readme) and relevant sections
-          required: true
-
   - type: markdown
     attributes:
       value: |
         ## Discussion Guidelines
-        
-        This is for general discussions about MeTube. For specific issues, please use:
-        - **Bug reports** → Use the Bug Report issue template
-        - **Feature requests** → Use the Feature Request issue template
-        - **Questions** → Use the Question issue template
+
+        This is for general discussions about MeTube. For specific topics, better homes exist:
+        - **Bug reports** → [open an issue](https://github.com/alexta69/metube/issues/new?template=bug_report.yml)
+        - **Feature requests** → [open an issue](https://github.com/alexta69/metube/issues/new?template=feature_request.yml) or post in [Ideas](https://github.com/alexta69/metube/discussions/categories/ideas)
+        - **Questions** → post in [Q&A](https://github.com/alexta69/metube/discussions/categories/q-a)
 
   - type: textarea
     id: discussion-topic
@@ -34,12 +17,3 @@ body:
       placeholder: Please provide a clear topic for discussion
     validations:
       required: true
-
-  - type: textarea
-    id: additional-context
-    attributes:
-      label: Additional Context
-      description: Any other information that might be helpful for the discussion
-      placeholder: Links, examples, or other relevant information
-    validations:
-      required: false