feat(chat): hide conversations + contact address picker for new conversation

Hide conversations:
- A "Hide" action in the thread header drops a conversation from the list. The
  messages stay in the seed-encrypted store (on-chain history can't be deleted);
  a new INCOMING message un-hides it (you can't un-receive), so nothing is lost.
- Hidden cids persist in settings (mirrors the mute list) and are skipped by both
  the conversation list and the unread badge.

New-conversation address picker:
- A "Choose from contacts" dropdown lists the address book's shielded (z-address)
  contacts and fills the recipient field on selection; manual paste still works.

8-language strings + CJK subset (+1 glyph 届).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/lang/zh.json

@@ -146,6 +146,8 @@
     "chat_export_done": "会话已导出",
     "chat_export_failed": "无法写入导出文件。",
     "chat_export_warn": "将解密后的消息保存为纯文本。请妥善保管该文件。",
+    "chat_hidden_toast": "会话已隐藏——收到新消息后会重新显示",
+    "chat_hide": "隐藏",
     "chat_jump_latest": "最新",
     "chat_len_over": "消息过长",
     "chat_locked_hint": "解锁钱包以加载您的聊天记录。",
@@ -157,6 +159,8 @@
     "chat_new_title": "新建对话",
     "chat_new_zaddr": "收款方 z 地址",
     "chat_no_matches": "没有与搜索匹配的会话。",
+    "chat_no_z_contacts": "暂无使用隐私地址的联系人",
+    "chat_pick_contact": "从联系人中选择…",
     "chat_retry": "重试",
     "chat_search": "搜索会话",
     "chat_select_hint": "选择一个对话以查看。",