docs: remove Numerical Conventions from README

Move technical detail out of the landing page. README now flows:
logo -> one-liner -> abstractions -> install -> usage -> operators -> links.
Numerical conventions remain in OPERATORS.md for users who need them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: quantbai

README.md

@@ -17,19 +17,6 @@ Polars-native factor computation engine for quantitative research. All operators
 - **`Panel`** -- Balanced `(timestamp, symbol)` container with strict alignment guarantees. Prevents look-ahead bias by construction.
 - **`Factor`** -- Immutable signal vector. Every operator takes `Factor` and returns `Factor` with eager evaluation.
 
-## Numerical Conventions
-
-| Convention | Summary |
-| --- | --- |
-| Null semantics | NaN/Inf unified to null on construction. Single missing-value type throughout. |
-| Division by zero | All divisions guarded at `abs(denom) < 1e-10`, returning null. |
-| Rank range | (0, 1] -- does not pass through zero. Ties use `average` method. |
-| Std/Variance/Covariance | ddof=0 (population). Correlation is ddof-invariant. |
-| Rolling warmup | All `ts_*` operators: first `window-1` values are null. |
-
-Full conventions and per-operator specifications:
-**[OPERATORS.md](OPERATORS.md)**
-
 ## Installation
 
 ```bash
@@ -80,6 +67,8 @@ panel = load("hourly.parquet", interval="1h")
 
 `add` `subtract` `multiply` `divide` `reverse` `densify` `bucket` and standard operators (`+` `-` `*` `/` `**` `abs`)
 
+Full specifications and numerical conventions: **[OPERATORS.md](OPERATORS.md)**
+
 ## Development
 
 ```bash