Add geohash bookmarks: persistence, sampling integration, and UI\n\n- Add GeohashBookmarksStore with UserDefaults persistence and toggle API\n- Sample union of regional + bookmarked geohashes for activity notifications\n- LocationChannelsSheet: bookmark icons on nearby rows and a Bookmarked section\n- Header toolbar: toggle bookmark for current geohash\n- Tests: GeohashBookmarksStoreTests for normalization and persistence\n\nRationale: Bookmarked geohashes are always sampled for new activity notifications and quickly selectable from the sheet.

bitchatTests/GeohashBookmarksStoreTests.swift

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+import XCTest
+@testable import bitchat
+
+final class GeohashBookmarksStoreTests: XCTestCase {
+    let storeKey = "locationChannel.bookmarks"
+
+    override func setUp() {
+        super.setUp()
+        // Clear persisted state before each test
+        UserDefaults.standard.removeObject(forKey: storeKey)
+        GeohashBookmarksStore.shared._resetForTesting()
+    }
+
+    override func tearDown() {
+        // Clean after each test
+        UserDefaults.standard.removeObject(forKey: storeKey)
+        GeohashBookmarksStore.shared._resetForTesting()
+        super.tearDown()
+    }
+
+    func testToggleAndNormalize() {
+        let store = GeohashBookmarksStore.shared
+        // Start clean
+        XCTAssertTrue(store.bookmarks.isEmpty)
+
+        // Add with mixed case and hash prefix
+        store.toggle("#U4PRUY")
+        XCTAssertTrue(store.isBookmarked("u4pruy"))
+        XCTAssertEqual(store.bookmarks.first, "u4pruy")
+
+        // Toggling again removes
+        store.toggle("u4pruy")
+        XCTAssertFalse(store.isBookmarked("u4pruy"))
+        XCTAssertTrue(store.bookmarks.isEmpty)
+    }
+
+    func testPersistenceWritten() throws {
+        let store = GeohashBookmarksStore.shared
+        store.toggle("ezs42")
+        store.toggle("u4pruy")
+
+        // Verify persisted JSON contains both (order not enforced here)
+        guard let data = UserDefaults.standard.data(forKey: storeKey) else {
+            XCTFail("No persisted data found")
+            return
+        }
+        let arr = try JSONDecoder().decode([String].self, from: data)
+        XCTAssertTrue(arr.contains("ezs42"))
+        XCTAssertTrue(arr.contains("u4pruy"))
+    }
+}