feat(pipeline): implement Pipeline DSL system for automated workflows

Add complete Pipeline DSL system including:
- Rust backend (zclaw-pipeline crate) with parser, executor, and state management
- Frontend components: PipelinesPanel, PipelineResultPreview, ClassroomPreviewer
- Pipeline recommender for Agent conversation integration
- 5 pipeline templates: education, marketing, legal, research, productivity
- Documentation for Pipeline DSL architecture

Pipeline DSL enables declarative workflow definitions with:
- YAML-based configuration
- Expression resolution (${inputs.topic}, ${steps.step1.output})
- LLM integration, parallel execution, file export
- Agent smart recommendations in conversations

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

crates/zclaw-pipeline/src/lib.rs

@@ -0,0 +1,56 @@
+//! ZCLAW Pipeline Engine
+//!
+//! Declarative pipeline system for multi-step automation workflows.
+//! Pipelines orchestrate Skills and Hands to accomplish complex tasks.
+//!
+//! # Architecture
+//!
+//! ```text
+//! Pipeline YAML → Parser → Pipeline struct → Executor → Output
+//!                              ↓
+//!                        ExecutionContext (state)
+//! ```
+//!
+//! # Example
+//!
+//! ```yaml
+//! apiVersion: zclaw/v1
+//! kind: Pipeline
+//! metadata:
+//!   name: classroom-generator
+//!   displayName: 互动课堂生成器
+//!   category: education
+//! spec:
+//!   inputs:
+//!     - name: topic
+//!       type: string
+//!       required: true
+//!   steps:
+//!     - id: parse
+//!       action: llm.generate
+//!       template: skills/classroom/parse.md
+//!       output: parsed
+//!     - id: render
+//!       action: classroom.render
+//!       input: ${steps.parse.output}
+//!       output: result
+//!   outputs:
+//!     classroom_id: ${steps.render.output.id}
+//! ```
+
+pub mod types;
+pub mod parser;
+pub mod state;
+pub mod executor;
+pub mod actions;
+
+pub use types::*;
+pub use parser::*;
+pub use state::*;
+pub use executor::*;
+pub use actions::ActionRegistry;
+
+/// Convenience function to parse pipeline YAML
+pub fn parse_pipeline_yaml(yaml: &str) -> Result<Pipeline, parser::ParseError> {
+    parser::PipelineParser::parse(yaml)
+}