Keyboard shortcut to switch between topics #1448

Feature Description

Add a keyboard shortcut to move to the next/previous topic in a topic-enabled chat (forum groups and topic-enabled bot DMs) without using the mouse.

Motivation

Telegram for macOS has shortcuts to move between chats (⌥⌘↑ / ⌥⌘↓) and folders (⌘1–9), but nothing to change topic once you are inside a forum chat. Switching topics currently requires clicking the topic list. That makes keyboard-only use of topic-heavy chats (including bot DMs with many topics) slow.

Related but not the same:

• Keyboard navigation (⌘K) into groups with topics enabled #1262 covers ⌘K landing in a topic group without a way to pick a topic
• Keyboard navigation broken when encountering group with topics #876 covers ⌥↑/⌥↓ chat navigation entering a topic group
• Alt + Arrow keys functionallity in the topic groups telegramdesktop/tdesktop#27960 asks for Alt+arrow behavior when entering a topic group, not switching topics inside one

Proposed Solution

• Next topic / previous topic bindings (user-remappable via Settings → General → Keyboard Shortcuts)
• Suggested defaults: ⌥⌘← / ⌥⌘→, or ⌥⌘[ / ⌥⌘]
• Operate on the current chat’s topic list (pinned first, then recency)
• Work in both forum groups and topic-enabled private chats

Alternatives Considered

• Relying on ⌘K: today it often opens the mixed “All topics” feed rather than a topic picker (Keyboard navigation (⌘K) into groups with topics enabled #1262)
• Pinning a few topics: still requires the mouse to switch

Additional Context

Native Telegram for Mac 12.x. Confirmed against the published shortcut list (TelegramSwift wiki): chat, folder, and search shortcuts exist; topic switch does not.