feat: add AyuGram-style Ghost Mode (WataGram settings)

[Seoul81]

Adds a new Ghost Mode feature set with four toggles, modeled after AyuGram:

• Don't send read receipts
• Don't send typing/recording/sticker activity
• Don't update online presence to the server
• Don't mark stories as seen

Storage:

• WataGramSettings (Codable) in TelegramUIPreferences with 4 Bool flags
• Registered as SharedDataKey add louder/longer alert sounds #23
• updateWataGramSettingsInteractively helper, mirroring the ExperimentalUISettings pattern

Plumbing:

• SharedAccountContext exposes immediateWataGramSettings; loaded via Atomic + accountManager.sharedData disposable
• SharedWakeupManager takes a closure getGhostHideOnline to read the flag without depending on SharedAccountContext directly

UI:

• WataGramSettingsController with four ItemListSwitchItem rows under a single Ghost Mode section + footer
• New .wataGram case in PeerInfoSettingsSection, with a row in the advanced section right under Privacy and Security

Gating:

• Read receipts: ChatHistoryListNode (6 sites) and applyMaxReadIndex callsite all check ghostModeReadReceipts
• Typing: ChatController activitySpace is set to nil when ghostModeTypingIndicator is on, suppressing typing/sticker/recording broadcasts uniformly
• Online: SharedWakeupManager.checkTasks gates shouldKeepOnlinePresence on ghostModeOnlineStatus
• Story-seen: 4 markAsSeen call sites in StoryChatContent gated on ghostModeStorySeen