[AIDAPP-1315]: Introduce pipeline stage classifications

[monali4-canyon]

Ticket(s) or GitHub Issue

• https://canyongbs.atlassian.net/browse/AIDAPP-1315

Technical Description

• New enum: PipelineStageClassification with Planning, InProgress, Complete cases
• Migration: Adds classification column to pipeline_stages table with Planning as the default for existing rows (uses initial() modifier)
• Feature flag: PipelineStageClassificationFeature gates the field visibility; activated during migration
• Model: Updated PipelineStage with classification in fillable and casts
• UI: Added classification Select (native) to the stages Repeater on Create, Edit, and Manage Pipelines pages; added badge display on View Pipeline
• Defaults: New pipelines are seeded with one stage per classification (Planning → In Progress → Complete)
• Factory/Request factories: Updated to include classification data
• Tests: PipelineStageClassificationTest covers enum values, model casting, DB persistence, and labels

Any deployment steps required?

No

Cleanup Tasks

Feature Flag Added: .cleanup-tasks/2026_07_14_pipeline_stage_classification_feature.md

---

Before contributing and submitting this PR, make sure you have Read, agree, and are compliant with the contributing guidelines.

[Orrison]

@rebecca-canyon please request my final review on this one once you have approved it.

Note that @monali4-canyon is going to be OOO tomorrow, so if there are any changes needed can you please make them directly on this branch?