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

tests/unit/web/feedback-links.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from "vitest";
+import {
+  buildFeedbackGithubUrl,
+  buildFeedbackMailtoUrl,
+  SNAPOTTER_FEEDBACK_EMAIL,
+} from "@/lib/feedback";
+
+describe("buildFeedbackGithubUrl", () => {
+  it("targets the feedback issue template and prefills the message", () => {
+    const url = buildFeedbackGithubUrl("The export button is slow");
+    expect(url).toContain("https://github.com/snapotter-hq/snapotter/issues/new");
+    expect(url).toContain("template=feedback.yml");
+    // URLSearchParams encodes spaces as "+"
+    expect(url).toContain("details=The+export+button+is+slow");
+  });
+
+  it("trims and clamps the message to 2000 characters", () => {
+    const url = buildFeedbackGithubUrl(`   hi   ${"x".repeat(2100)}`);
+    const details = new URL(url).searchParams.get("details") ?? "";
+    expect(details.startsWith("hi")).toBe(true);
+    expect(details.length).toBeLessThanOrEqual(2000);
+  });
+});
+
+describe("buildFeedbackMailtoUrl", () => {
+  it("builds a mailto to the project address with an encoded body", () => {
+    const url = buildFeedbackMailtoUrl("Love the app, one bug");
+    expect(url.startsWith(`mailto:${SNAPOTTER_FEEDBACK_EMAIL}`)).toBe(true);
+    expect(url).toContain("subject=SnapOtter%20feedback");
+    expect(url).toContain("body=Love%20the%20app%2C%20one%20bug");
+  });
+
+  it("uses contact@snapotter.com", () => {
+    expect(SNAPOTTER_FEEDBACK_EMAIL).toBe("contact@snapotter.com");
+  });
+});