Epic: Scenario Planning - integrate with portfolio, FIRE, and Monte Carlo

[unav4ila8le]

Umbrella epic to track integration of Scenario Planning with user portfolios, add FIRE mode, and add Monte Carlo simulations. Tracks overall metrics and rollout plan.

Sub-issues:

• Quick win: Auto-fill starting balance and persist scenarios (Quick win: Auto-fill starting balance and persist scenarios #153)
• Return presets + UI preset selector (equities and global) (Return presets + UI preset selector (equities and global) #154)
• Use my portfolio mode - deterministic per-asset simulation (FIRE calculator mode - deterministic time-to-target and SWR sensitivity #155)
• FIRE calculator mode - deterministic time-to-target and SWR sensitivity (FIRE calculator mode - deterministic time-to-target and SWR sensitivity #155 )
• Monte Carlo server-side simulation and caching (Monte Carlo server-side simulation and caching #156 )