Virtual F&O trading with lot sizes and margin estimates

[iamsaquib8]

What

Options and futures are where beginners lose most money. Practising them in the simulator first, with real lot sizes and margins, is a safe way to learn.

Scope

• stockwise sim fno buy NIFTY 24500 CE --expiry 2026-11-27 --lots 1; futures too.
• Lot sizes from NSE's published list (cached), premiums from the option chain already used by options chain, expiry settlement at the underlying's close.
• Margin estimates for short positions (SPAN-like approximation, clearly labelled as an estimate), and a warning when a position would exceed the virtual account's margin.
• Greeks and P&L per position; replay support later.

Done when

• A position's P&L at expiry matches the payoff from options payoff (tests).
• Short positions show a margin estimate and are refused beyond the account's capital.

---

Moved from issue #268 to keep the issue tracker for scheduled work. Upvote or comment if you would use this; ideas with demand go back on the roadmap.