chore: add issue templates (bug + feature)

Gitea-native yaml templates for web UI, local markdown copy for reference.

.gitea/issue_template/bug.yaml

@@ -0,0 +1,29 @@
+name: Bug
+about: Something broken
+body:
+  - type: input
+    id: what
+    attributes:
+      label: What happened
+      placeholder: "stream entries disappear at mobile breakpoint"
+    validations:
+      required: true
+  - type: input
+    id: expected
+    attributes:
+      label: Expected
+      placeholder: "entries stay visible when viewport narrows"
+  - type: dropdown
+    id: area
+    attributes:
+      label: Area
+      options:
+        - ui
+        - api
+        - data
+        - other
+  - type: input
+    id: repro
+    attributes:
+      label: Repro steps (if not obvious)
+      placeholder: "zoom to 67%, press z twice"