feat: migrate from Docker to pixi for BtToxin_Digger execution

- Add pixi.toml with digger and pipeline environments
- Implement PixiRunner class replacing DockerContainerManager
- Add run_digger_stage.py for standalone digger execution
- Update run_single_fna_pipeline.py to use PixiRunner
- Remove docker dependency from pyproject.toml
- Delete docker_client.py (no longer needed)

BREAKING CHANGE: Docker is no longer required. Use 'pixi install' instead.

pixi.toml

@@ -0,0 +1,43 @@
+[workspace]
+name = "bttoxin-pipeline"
+channels = ["conda-forge", "bioconda", "bioconda/label/cf201901"]
+platforms = ["linux-64"]
+version = "0.1.0"
+channel-priority = "disabled"
+
+# =========================
+# digger 环境：bioconda 依赖
+# =========================
+[feature.digger.dependencies]
+bttoxin_digger = "==1.0.10"
+perl = "==5.26.2"
+perl-file-tee = "==0.07"
+perl-list-util = "==1.38"
+blast = "==2.16.0"
+
+# =========================
+# pipeline 环境：Python 分析依赖
+# =========================
+[feature.pipeline.dependencies]
+python = ">=3.9"
+pandas = ">=2.0.0"
+matplotlib = ">=3.7.0"
+seaborn = ">=0.12.2"
+
+# =========================
+# 环境定义
+# =========================
+[environments]
+digger = ["digger"]
+pipeline = ["pipeline"]
+
+# =========================
+# pixi tasks
+# =========================
+[feature.pipeline.tasks]
+# 完整 pipeline（三阶段）
+pipeline = "python scripts/run_single_fna_pipeline.py"
+# 单独阶段
+digger-only = "python scripts/run_digger_stage.py"
+shotter = "python scripts/bttoxin_shoter.py"
+plot = "python scripts/plot_shotter.py"