Add custom API URL and model to AI settings

- Settings → AI: optional base URL and model name fields
- Defaults to Anthropic/OpenAI public APIs when left blank
- Custom URL enables Open WebUI, LM Studio, Ollama, and any OpenAI-compatible endpoint
- Parse endpoint uses custom base URL and model if configured
- Migration 0004: ai_base_url + ai_model columns on users
- OpenAI provider label updated to "OpenAI-compatible"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/v1/settings.py

@@ -20,11 +20,15 @@ SUPPORTED_PROVIDERS = {"anthropic", "openai"}
 class AiSettingsResponse(BaseModel):
     provider: str | None
     has_api_key: bool
+    base_url: str | None
+    model: str | None
 
 
 class AiSettingsSave(BaseModel):
     provider: str
-    api_key: str
+    api_key: str = ""
+    base_url: str = ""
+    model: str = ""
 
 
 @router.get("/ai", response_model=AiSettingsResponse)
@@ -32,6 +36,8 @@ async def get_ai_settings(user: User = Depends(get_current_user)):
     return AiSettingsResponse(
         provider=user.ai_provider,
         has_api_key=bool(user.ai_api_key_enc),
+        base_url=user.ai_base_url,
+        model=user.ai_model,
     )
 
 
@@ -43,17 +49,26 @@ async def save_ai_settings(
 ):
     if body.provider not in SUPPORTED_PROVIDERS:
         raise HTTPException(status_code=400, detail=f"Unsupported provider. Choose: {', '.join(SUPPORTED_PROVIDERS)}")
-    if not body.api_key.strip():
-        raise HTTPException(status_code=400, detail="api_key must not be empty")
 
-    encrypted = encrypt_field(body.api_key.strip())
-    await db.execute(
-        update(User)
-        .where(User.id == user.id)
-        .values(ai_provider=body.provider, ai_api_key_enc=encrypted)
-    )
+    values: dict = {
+        "ai_provider": body.provider,
+        "ai_base_url": body.base_url.rstrip("/") or None,
+        "ai_model": body.model.strip() or None,
+    }
+
+    if body.api_key.strip():
+        values["ai_api_key_enc"] = encrypt_field(body.api_key.strip())
+    elif not user.ai_api_key_enc:
+        raise HTTPException(status_code=400, detail="api_key is required when no key is saved yet")
+
+    await db.execute(update(User).where(User.id == user.id).values(**values))
     await db.commit()
-    return AiSettingsResponse(provider=body.provider, has_api_key=True)
+    return AiSettingsResponse(
+        provider=body.provider,
+        has_api_key=True,
+        base_url=values["ai_base_url"],
+        model=values["ai_model"],
+    )
 
 
 @router.delete("/ai", status_code=204)
@@ -64,6 +79,6 @@ async def clear_ai_settings(
     await db.execute(
         update(User)
         .where(User.id == user.id)
-        .values(ai_provider=None, ai_api_key_enc=None)
+        .values(ai_provider=None, ai_api_key_enc=None, ai_base_url=None, ai_model=None)
     )
     await db.commit()