feat: implement essential numeric and logical builtin functions (issue #12)

Adds 13 WGSL builtin functions:

Numeric functions:
- dot: Dot product for Vec{2,3,4}f/i/u
- normalize: Unit vector for Vec{2,3,4}f
- cross: Cross product for Vec3f
- clamp: Value clamping for f32/i32/u32 and vectors
- mix: Linear interpolation for f32 and Vec{2,3,4}f
- floor: Floor for f32 and Vec{2,3,4}f
- ceil: Ceiling for f32 and Vec{2,3,4}f
- exp: Natural exponentiation for f32 and Vec{2,3,4}f
- exp2: Base-2 exponentiation for f32 and Vec{2,3,4}f
- degrees: Radians to degrees for f32 and Vec{2,3,4}f

Logical functions:
- all: Returns true if all components are true (Vec{2,3,4}b)
- any: Returns true if any component is true (Vec{2,3,4}b)
- select: Conditional select for all scalar and vector types

Closes #12

Author: schell

SESSION.md

@@ -0,0 +1,63 @@
+# Session: Essential Numeric and Logical Builtin Functions
+
+## Selected Issue
+
+**Issue #12 - Essential Numeric and Logical Builtin Functions (Priority 1)**
+https://github.com/schell/wgsl-rs/issues/12
+
+## Functions Implemented
+
+### Numeric Functions (10)
+- [x] `dot(e1: vecN<T>, e2: vecN<T>) -> T` - Dot product
+- [x] `normalize(e: vecN<T>) -> vecN<T>` - Unit vector
+- [x] `cross(e1: vec3<T>, e2: vec3<T>) -> vec3<T>` - Cross product (vec3 only)
+- [x] `clamp(e: T, low: T, high: T) -> T` - Value clamping
+- [x] `mix(e1: T, e2: T, e3: T) -> T` - Linear interpolation
+- [x] `floor(e: T) -> T` - Floor
+- [x] `ceil(e: T) -> T` - Ceiling
+- [x] `exp(e: T) -> T` - Natural exponentiation (e^x)
+- [x] `exp2(e: T) -> T` - Base-2 exponentiation (2^x)
+- [x] `degrees(e: T) -> T` - Radians to degrees
+
+### Logical Functions (3)
+- [x] `all(e: vecN<bool>) -> bool` - Returns true if all components are true
+- [x] `any(e: vecN<bool>) -> bool` - Returns true if any component is true
+- [x] `select(f: T, t: T, cond: bool) -> T` - Conditional select
+
+## Type Support
+
+| Function | f32 | i32 | u32 | Vec{2,3,4}f | Vec{2,3,4}i | Vec{2,3,4}u | Vec{2,3,4}b |
+|----------|-----|-----|-----|-------------|-------------|-------------|-------------|
+| dot | - | - | - | Yes | Yes | Yes | - |
+| normalize | - | - | - | Yes | - | - | - |
+| cross | - | - | - | Vec3f only | - | - | - |
+| clamp | Yes | Yes | Yes | Yes | Yes | Yes | - |
+| mix | Yes | - | - | Yes | - | - | - |
+| floor | Yes | - | - | Yes | - | - | - |
+| ceil | Yes | - | - | Yes | - | - | - |
+| exp | Yes | - | - | Yes | - | - | - |
+| exp2 | Yes | - | - | Yes | - | - | - |
+| degrees | Yes | - | - | Yes | - | - | - |
+| all | - | - | - | - | - | - | Yes (returns bool) |
+| any | - | - | - | - | - | - | Yes (returns bool) |
+| select | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
+
+## Implementation Summary
+
+### File Modified
+`crates/wgsl-rs/src/std/numeric_builtin_functions.rs`
+
+### Changes Made
+1. Added 13 new trait/function pairs
+2. Added 13 sanity tests
+3. Updated doc comment table to mark all 13 functions as implemented (`x`)
+
+### Verification
+- `cargo test` - 39 tests pass (13 new)
+- `cargo clippy` - No warnings
+- `cargo fmt` - Applied
+
+## Reference
+
+- WGSL Spec Numeric: https://gpuweb.github.io/gpuweb/wgsl/#numeric-builtin-functions
+- WGSL Spec Logical: https://gpuweb.github.io/gpuweb/wgsl/#logical-builtin-functions