feat(pipeline): add sequential task pipeline engine with data passing

[JeremyDev87]

Summary

• Add sequential task pipeline engine that chains stages with data passing (A→B→C)
• Each stage can be a shell command, agent prompt, or skill invocation
• Output from stage N is automatically passed as input to stage N+1
• Pipeline resumes from failed stage (not restart from beginning)
• Status tracking with per-stage results, timing, and progress
• 3 MCP tools: run_pipeline, pipeline_status, resume_pipeline
• New pipeline/ module following existing NestJS + AbstractHandler patterns
• 51 new tests (types, executors, service, handler), all passing

Test plan

• 18 type guard tests (isValidStageType, isValidPipelineStage, isValidPipelineDefinition)
• 9 executor tests (command/agent/skill stages, error handling, timing)
• 12 service tests (sequential execution, data passing, resume, edge cases)
• 12 handler tests (MCP tool validation, error responses, tool definitions)
• Full CI: lint, format, typecheck, test:coverage (5023 pass), circular, build

Closes #814

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Project	Deployment	Actions	Updated (UTC)
codingbuddy-landing	Ready	Preview, Comment	Mar 24, 2026 3:58pm