feat: add full derivatives analytics layer (options + futures)

Implements all phases of the derivatives expansion plan:

Rust core (crates/ferro_ta_core/src/options/, src/futures/):
- BSM and Black-76 pricing (scalar + vectorized batch)
- Greeks: delta, gamma, vega, theta, rho
- Implied volatility solver (Newton + bisection fallback)
- Smile/skew metrics: ATM IV, 25-delta RR/BF, skew slope, convexity
- Chain helpers: moneyness labels, strike selection by offset or delta
- Synthetic forwards, basis, annualized basis, implied carry, carry spread
- Continuous contract stitching: weighted, back-adjusted, ratio-adjusted
- Curve analytics: calendar spreads, slope, contango/backwardation summary

PyO3 bindings (src/options/, src/futures/):
- All Rust functions registered and exposed via _ferro_ta extension

Python API (python/ferro_ta/analysis/):
- options.py: pricing, greeks, IV, smile, chain, legacy iv_rank/percentile/zscore
- futures.py: basis, carry, curve, roll, synthetic, continuous contracts
- options_strategy.py: typed strategy schemas (expiry/strike selectors, leg presets, risk controls, simulation limits)
- derivatives_payoff.py: multi-leg payoff aggregation and Greeks aggregation

Bug fix: wrap _to_f64 calls in iv_rank/iv_percentile/iv_zscore to raise
FerroTAInputError (not plain ValueError) for 2D array input.

Docs: derivatives.rst, derivatives-analytics.md, options-volatility.md,
quickstart.rst, index.rst, api/analysis.rst all updated.

Tests: 2053 pass, 12 skipped. All CI checks pass locally.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/index.rst

@@ -13,6 +13,7 @@ ferro-ta Documentation
    streaming
    extended
    batch
+   derivatives
    benchmarks
    plugins
    changelog
@@ -35,7 +36,7 @@ Features:
 - Math operators and transforms
 - Type stubs (.pyi) for IDE auto-completion
 - WASM binding for browser/Node.js use
-- Options/IV helpers (IV rank, IV percentile, IV z-score) — see `Options/IV Helpers <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/options-volatility.md>`_
+- Options/IV helpers and derivatives analytics — see :doc:`derivatives`
 - Agentic workflow and LangChain tool wrappers — see `Agentic guide <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/agentic.md>`_
 - MCP server for Cursor/Claude integration — see `MCP guide <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/mcp.md>`_
 - Sphinx documentation
@@ -71,7 +72,7 @@ Further Reading
 - `API Stability <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/stability.md>`_ — stability tiers, versioning, and deprecation policy.
 - `Rust-First Policy <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/rust_first.md>`_ — all compute logic belongs in Rust; how to add new indicators.
 - `Out-of-Core Execution <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/out-of-core.md>`_ — chunked processing and Dask integration.
-- `Options/IV Helpers <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/options-volatility.md>`_ — IV rank, IV percentile, IV z-score.
+- :doc:`derivatives` — IV helpers, options pricing/Greeks/IV, futures analytics, strategy schemas, and payoff helpers.
 - `Agentic Workflow <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/agentic.md>`_ — tools.py, workflow.py, LangChain integration.
 - `MCP Server <https://github.com/pratikbhadane24/ferro-ta/blob/main/docs/mcp.md>`_ — run ferro-ta as an MCP server in Cursor/Claude.