feat(feedback): always-on nav button with GitHub/email handoff when analytics is off (#428)

Keep the top-nav feedback button always visible (icon plus label on desktop, icon-only on mobile) instead of hiding it when an instance opts out of analytics. When analytics is off, the dialog keeps the typed message and hands off to a prefilled GitHub issue plus a contact@snapotter.com email, with no fake Thanks. Adds a feedback.yml issue template, URL builders, and feedback strings across all 21 locales.

Claude-Session: https://claude.ai/code/session_01XVrHKXwzZDWBWgkGQdPZ3A

.github/ISSUE_TEMPLATE/feedback.yml

@@ -0,0 +1,16 @@
+name: General feedback
+description: Share general feedback, ideas, or reactions about SnapOtter.
+title: "[Feedback]: "
+labels: ["feedback"]
+body:
+  - type: markdown
+    attributes:
+      value: Thanks for taking a moment to share feedback.
+  - type: textarea
+    id: details
+    attributes:
+      label: Your feedback
+      description: What is on your mind?
+      placeholder: Tell us what you think...
+    validations:
+      required: true