feat: add account deletion feature (#85)

* feat: add account deletion feature

- Add DELETE /auth/me endpoint to delete user account and all data
- Add deleteAccount() method to AuthContext
- Add Delete Account button with confirmation modal in UserProfile
- Add danger zone styling (.btn-danger, .profile-danger-zone)
- Add i18n translations for EN and DE
- Add backend tests for account deletion endpoint
- Add timeout settings to frontend vitest.config.ts
- Reduce CI timeout for frontend tests (10min -> 5min)

* fix: improve delete account section layout

- Make profile modal scrollable with max-height
- Add proper horizontal margin to danger zone
- Align delete section with form content

* fix: use ConfirmModal component for delete account dialog

- Replace inline modal with existing ConfirmModal component
- Ensures consistent button styling across all modals
- Add UI consistency rule to AGENTS.md and copilot-instructions.md

* fix: consistent styling for delete account section

- Remove warning text (users know what delete means)
- Remove border-bottom from danger zone title (section has border-top)
- Update copilot-instructions and AGENTS.md with stricter UI consistency rules
- Remove unused deleteAccountHint i18n keys

* chore: remove pre-push test hook (CI handles tests)

Tests were running twice - in pre-push hook and GitHub CI.
Removing local pre-push tests since CI provides authoritative test results.
Use 'npm test' manually before pushing if you want local feedback.

backend/src/test/auth.test.ts

@@ -682,4 +682,62 @@ describe("Auth Routes (AUTH_ENABLED=true)", () => {
 			expect(response.statusCode).toBe(401);
 		});
 	});
+
+	describe("DELETE /auth/me - Delete Account", () => {
+		it("should delete user account and all data", async () => {
+			// Register and login
+			await app.inject({
+				method: "POST",
+				url: "/auth/register",
+				payload: {
+					username: "deleteuser",
+					password: "TestPassword123",
+				},
+			});
+
+			const login = await app.inject({
+				method: "POST",
+				url: "/auth/login",
+				payload: {
+					username: "deleteuser",
+					password: "TestPassword123",
+				},
+			});
+
+			const accessToken = login.cookies.find((c: any) => c.name === "access_token");
+
+			// Delete account
+			const response = await app.inject({
+				method: "DELETE",
+				url: "/auth/me",
+				cookies: {
+					access_token: accessToken?.value ?? "",
+				},
+			});
+
+			expect(response.statusCode).toBe(200);
+			expect(response.json().ok).toBe(true);
+
+			// Verify can't login anymore
+			const loginAgain = await app.inject({
+				method: "POST",
+				url: "/auth/login",
+				payload: {
+					username: "deleteuser",
+					password: "TestPassword123",
+				},
+			});
+
+			expect(loginAgain.statusCode).toBe(401);
+		});
+
+		it("should reject delete without auth", async () => {
+			const response = await app.inject({
+				method: "DELETE",
+				url: "/auth/me",
+			});
+
+			expect(response.statusCode).toBe(401);
+		});
+	});
 });