Remove hardcoded DeepSeek-OCR model default value

[Copilot]

DeepSeek-OCR model name was hardcoded as default in DeepSeekOCRConfig, limiting model flexibility despite DS_OCR_MODEL env var support.

Changes

• Make model field required (no default) in DeepSeekOCRConfig, consistent with api_key
• Users must explicitly set DS_OCR_MODEL in .env (already present in env.example)

# Before
model: str = Field(
    default="deepseek-ai/DeepSeek-OCR",
    description="DeepSeek-OCR Model Name"
)

# After
model: str = Field(..., description="DeepSeek-OCR Model Name")

Original prompt

---

This section details on the original issue you should resolve

<issue_title>DeepSeek-OCR model name hardcoded - limits model flexibility</issue_title>
<issue_description>## 问题描述
DeepSeek-OCR 模型名称硬编码，限制模型灵活性。

受影响的文件

• src/config.py 行 102

硬编码值

• default="deepseek-ai/DeepSeek-OCR"

问题

虽然有 DS_OCR_MODEL 环境变量，但代码默认值也硬编码。

解决方案

应该保持一致，建议移除硬编码的默认值。</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes DeepSeek-OCR model name hardcoded - limits model flexibility #17

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[Copilot]

Pull request overview

This PR removes the hardcoded default value for the DeepSeek-OCR model name in the configuration, making it a required field that must be explicitly set via the DS_OCR_MODEL environment variable. The change aims to improve model flexibility by eliminating the hardcoded default value while relying on users to configure this in their .env file (as shown in env.example).

Key Changes:

• Changed model field in DeepSeekOCRConfig from having a default value ("deepseek-ai/DeepSeek-OCR") to being required (Field(...))
• Users must now explicitly set DS_OCR_MODEL in their .env file for the application to start

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[Copilot]

Making the model field required creates an inconsistency with other configuration classes in this codebase. LLMConfig (line 24), EmbeddingConfig (line 46-49), and RerankConfig (line 74-77) all provide default values for their model fields.

This inconsistency means that:

1. Users must explicitly set DS_OCR_MODEL or the application will fail to start
2. Other services can start with sensible defaults even if their model env vars are missing
3. The configuration pattern is not uniform across the codebase

Consider either:

• Keeping the default value to maintain consistency with other configs
• Or updating all other config classes to also require explicit model specification (if that's the desired pattern)

Suggested change

	model: str = Field(..., description="DeepSeek-OCR Model Name")
	model: str = Field(default="deepseek-ocr-base", description="DeepSeek-OCR Model Name")