feat: add GPU acceleration support OpenSpec proposal

新增 GPU 加速支援的 OpenSpec 變更提案

主要內容：
- 在環境建置腳本中加入 GPU 偵測功能
- 自動安裝對應 CUDA 版本的 PaddlePaddle GPU 套件
- 在 OCR 處理程式中加入 GPU 可用性偵測
- 自動啟用 GPU 加速（可用時）或使用 CPU（不可用時）
- 支援強制 CPU 模式選項
- 加入 GPU 狀態報告到健康檢查 API

變更範圍：
- 新增 capability: environment-setup (環境設置)
- 修改 capability: ocr-processing (加入 GPU 支援)

實作任務包含：
1. 環境設置腳本增強 (GPU 偵測、CUDA 安裝)
2. 配置更新 (GPU 相關環境變數)
3. OCR 服務 GPU 整合 (自動偵測、記憶體管理)
4. 健康檢查與監控 (GPU 狀態報告)
5. 文檔更新
6. 測試與效能評估
7. 錯誤處理與邊界情況

預期效果：
- GPU 系統: 3-10x OCR 處理速度提升
- CPU 系統: 無影響，向後相容
- 自動硬體偵測與優化配置

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

openspec/changes/add-gpu-acceleration-support/specs/environment-setup/spec.md

@@ -0,0 +1,77 @@
+# Environment Setup Specification
+
+## ADDED Requirements
+
+### Requirement: GPU Detection and CUDA Installation
+The system SHALL automatically detect compatible GPU hardware during environment setup and install appropriate PaddlePaddle packages (GPU-enabled or CPU-only) based on hardware availability.
+
+#### Scenario: GPU detected with CUDA support
+- **WHEN** setup script runs on system with NVIDIA GPU and CUDA drivers
+- **THEN** the script detects GPU using `nvidia-smi` command
+- **AND** determines CUDA version from driver
+- **AND** installs `paddlepaddle-gpu` with matching CUDA version
+- **AND** verifies GPU availability through Python
+- **AND** displays GPU information (device name, CUDA version, memory)
+
+#### Scenario: No GPU detected
+- **WHEN** setup script runs on system without compatible GPU
+- **THEN** the script detects absence of GPU hardware
+- **AND** installs CPU-only `paddlepaddle` package
+- **AND** displays message that CPU mode will be used
+- **AND** continues setup without errors
+
+#### Scenario: GPU detected but no CUDA drivers
+- **WHEN** setup script detects NVIDIA GPU but CUDA drivers are missing
+- **THEN** the script displays warning about missing drivers
+- **AND** provides installation instructions for CUDA drivers
+- **AND** falls back to CPU-only installation
+- **AND** suggests re-running setup after driver installation
+
+#### Scenario: CUDA version mismatch
+- **WHEN** detected CUDA version is not compatible with available PaddlePaddle packages
+- **THEN** the script displays available CUDA versions
+- **AND** installs closest compatible PaddlePaddle GPU package
+- **AND** warns user about potential compatibility issues
+- **AND** provides instructions to upgrade/downgrade CUDA if needed
+
+#### Scenario: Manual CUDA version override
+- **WHEN** user sets CUDA_VERSION environment variable before running setup
+- **THEN** the script uses specified CUDA version instead of auto-detection
+- **AND** installs corresponding PaddlePaddle GPU package
+- **AND** skips automatic CUDA detection
+- **AND** displays warning if specified version differs from detected version
+
+### Requirement: GPU Verification
+The system SHALL verify GPU functionality after installation and provide clear status reporting.
+
+#### Scenario: Successful GPU setup verification
+- **WHEN** PaddlePaddle GPU installation completes
+- **THEN** the script runs GPU availability test using Python
+- **AND** confirms CUDA devices are accessible
+- **AND** displays GPU count, device names, and memory capacity
+- **AND** marks GPU setup as successful
+
+#### Scenario: GPU verification fails
+- **WHEN** GPU verification test fails after installation
+- **THEN** the script displays detailed error message
+- **AND** provides troubleshooting steps
+- **AND** suggests fallback to CPU mode
+- **AND** does not fail entire setup process
+
+### Requirement: Environment Configuration for GPU
+The system SHALL create appropriate configuration settings for GPU usage in environment files.
+
+#### Scenario: GPU-enabled configuration
+- **WHEN** GPU is successfully detected and verified
+- **THEN** the setup script adds GPU settings to `.env.local`
+- **AND** sets `FORCE_CPU_MODE=false`
+- **AND** sets detected `CUDA_VERSION`
+- **AND** sets recommended `GPU_MEMORY_FRACTION` (e.g., 0.8)
+- **AND** adds GPU-related comments and documentation
+
+#### Scenario: CPU-only configuration
+- **WHEN** no GPU is detected or verification fails
+- **THEN** the setup script creates CPU-only configuration
+- **AND** sets `FORCE_CPU_MODE=true`
+- **AND** omits or comments out GPU-specific settings
+- **AND** adds note about GPU requirements