Add multi-plan graduation workspaces

[PMN123]

What changed

• Added three independent, browser-local graduation-target workspaces.
• Added true in-term course sorting, live target horizon status, and optional secondary CS focus support.
• Kept the CS + Mathematics + Statistics (Mathematics Emphasis) + Finance-minor combination available as a one-click setup.

Why

Comparing Spring 2028, Fall 2028, and Spring 2029 schedules needs isolated plans without exposing personal academic data.

Validation

• npm run build
• Python scaffold/audit check across the four selected programs and all three target terms
• python3 -m py_compile webapp/scheduler.py webapp/server.py