feat(api): use Tencent 16k_zh_large ASR and remove local Whisper

Standardize ASR on Tencent's dialect-capable engine across all environments,
drop faster-whisper from dependencies and deployment images, and add an
expo-sqlite iOS vendor sync plus pod install in prebuild to prevent native
build failures after npm install.

Co-authored-by: Cursor <cursoragent@cursor.com>

api/app/core/app_config_models.py

@@ -1,5 +1,7 @@
 """Pydantic models for TOML-backed application configuration (non-secret SSOT)."""
 
+from typing import Literal
+
 from pydantic import BaseModel, ConfigDict, Field
 
 
@@ -201,11 +203,8 @@ class LlmConfig(BaseModel):
 class AsrConfig(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
-    provider: str = "whisper"
-    model_size: str = "small"
-    device: str = "auto"
-    compute_type: str = "auto"
-    model_cache_dir: str = ""
+    provider: Literal["tencent"] = "tencent"
+    engine_type: Literal["16k_zh_large"] = "16k_zh_large"
 
 
 class TtsConfig(BaseModel):