feat(gateway): inline choice pickers for /reasoning and /fast (Telegram, Discord, Matrix) (#65799)

Bare /reasoning and /fast now render a native one-tap picker on
picker-capable platforms, with automatic fallback to the text status
card everywhere else — parity with the /model picker UX.

- gateway/slash_commands.py: generic send_choice_picker capability gate
  (detected on the adapter type, like send_model_picker); selection and
  typed arguments flow through one shared application path so they can
  never diverge; choices built from VALID_REASONING_EFFORTS so future
  levels appear automatically
- telegram: flat inline-keyboard picker (cp:<idx> callbacks), authorized
  users only (same gate as approval buttons)
- discord: ChoicePickerView select menu, auth mirrors ExecApprovalView,
  2-minute timeout with expiry edit
- matrix: reaction-based picker; reaction set extended to 12 slots to
  fit the full effort ladder + subcommands
- locales: picker_title + choice labels in all 16 languages
- docs: ADDING_A_PLATFORM.md capability table

Closes #61110.

locales/zh-hant.yaml

@@ -124,6 +124,9 @@ gateway:
     label_normal:          "NORMAL"
     status_fast:           "fast"
     status_normal:         "normal"
+    picker_title:          "⚡ **Priority Processing**\\n\\n目前模式：`{mode}`\\n\\n請選擇："
+    choice_fast:           "fast — 開啟 Priority Processing"
+    choice_normal:         "normal — 標準處理"
 
   footer:
     status:                "📎 執行階段頁尾：**{state}**\n欄位：`{fields}`\n平台：`{platform}`"
@@ -194,6 +197,11 @@ gateway:
     reset_global_unsupported:  "⚠️ 不支援 `/reasoning reset --global`。請使用 `/reasoning <level> --global` 變更全域預設值。"
     reset_done:                "🧠 ✓ 已清除本工作階段的推理覆寫；回退至全域設定。"
     unknown_arg:               "⚠️ 未知參數：`{arg}`\n\n**有效級別：** none, minimal, low, medium, high, xhigh, max, ultra\n**顯示：** show, hide\n**持久化：** 加上 `--global` 可跨工作階段儲存"
+    picker_title:              "🧠 **推理設定**\\n\\n**強度：** `{level}`\\n**範圍：** {scope}\\n**顯示：** {display}\\n\\n請選擇："
+    choice_none:               "none — 停用推理"
+    choice_reset:              "reset — 清除工作階段覆寫"
+    choice_show:               "在回覆中顯示推理"
+    choice_hide:               "在回覆中隱藏推理"
     set_global:                "🧠 ✓ 推理強度已設定為 `{effort}`（已儲存到設定）\n_（下一則訊息生效）_"
     set_global_save_failed:    "🧠 ✓ 推理強度已設定為 `{effort}`（僅本工作階段 — 設定儲存失敗）\n_（下一則訊息生效）_"
     set_session:               "🧠 ✓ 推理強度已設定為 `{effort}`（僅本工作階段 — 加上 `--global` 可持久化）\n_（下一則訊息生效）_"