feat(issues): add platform dropdown to all issue templates

Adds Linux/macOS selection as first field in bug reports, feature
requests, and feedback forms. Adapts Linux-specific fields (DE, display
server) to indicate they are Linux-only and adds macOS options to
install method and audio backend dropdowns.

cc

.github/ISSUE_TEMPLATE/feedback.yml

@@ -3,6 +3,17 @@ description: General feedback, UX thoughts, or non-bug discussion
 title: "[Feedback] "
 labels: ["feedback"]
 body:
+  - type: dropdown
+    id: platform
+    attributes:
+      label: Platform
+      options:
+        - ""
+        - Linux
+        - macOS
+    validations:
+      required: false
+
   - type: textarea
     id: feedback
     attributes:
@@ -25,7 +36,7 @@ body:
     id: version
     attributes:
       label: QBZ version (optional)
-      placeholder: e.g. v1.1.20
+      placeholder: e.g. v1.2.0
 
   - type: dropdown
     id: install
@@ -37,15 +48,17 @@ body:
         - .deb
         - .rpm
         - AUR
+        - Gentoo overlay
         - Tarball
         - Flatpak
+        - DMG (macOS)
         - Built from source
 
   - type: input
     id: distro
     attributes:
-      label: Distribution (optional)
-      placeholder: e.g. Arch Linux, Ubuntu 24.04
+      label: Distribution / macOS version (optional)
+      placeholder: e.g. Arch Linux, Ubuntu 24.04, macOS 15.3 Sequoia
 
   - type: textarea
     id: notes