Turn Pipeline tab into a task-oriented guided workflow for first-time users

[nikolareljin]

ID: KF-011

The current Pipeline tab (see KF-009) improves tab ordering, but it
still assumes the user already understands dataset capture, reconstruction, and
mesh viewing. From a user perspective, the app does not answer basic questions:
"what do I do first?", "what did this step produce?", "what does success look
like?", and "what should I do next?". This causes complete workflow confusion
even when the underlying features work.

Fix: extend the Pipeline tab into a guided workflow with plain-language step
cards and explicit next actions:

1. Check camera, confirm live feed
2. Frame object, choose isolation settings
3. Capture scan frames
4. Build 3D model
5. Review and export result

Each step must include:

• short explanation of user goal
• visible prerequisites
• completion criteria
• one primary CTA
• next-step text after completion

Add a persistent session summary panel showing current scan folder, saved frame
count, chosen preset, output mesh path, and whether the app is in capture-ready,
reconstruct-ready, or result-ready state. On unsupported platforms, show a
reconstruct-only workflow instead of presenting unavailable capture actions.

This is an extension of KF-009, not a duplicate. KF-009 created a tab; this
issue makes that tab product-grade and decision-free for end users.

Files: src/kinect_forge/gui.py, docs/GUI.md, docs/USER_GUIDE.md

References:

• Original issue: Add Pipeline tab as guided entry point in GUI #9
• Progressive disclosure guidance: https://www.nngroup.com/articles/progressive-disclosure/
• Stepper workflow reference: https://m3.material.io/components/steppers/overview