The user wants a procedural L-system fractal tree using p5.js (already provided as p5.min.js). Requirements:
- Single index.html file
- Self-contained, no external resources except p5.min.js loaded locally
- L-system fractal tree that branches recursively
- Gentle swaying in the wind effect
- CSS in <style>, JS in <script>

I need to create an L-system implementation. The L-system will have:
- Axiom (start string)
- Production rules (e.g., F -> F[+F]F[-F]F or similar for branching)
- Angle for turning
- Length for segments
- Iterations to generate the string

For the swaying effect, I'll use a time-based offset (sin/cos functions) applied to the rotation angles, simulating wind. I can use noise() or sin() for organic movement.

Structure:
1. HTML boilerplate
2. CSS for full-screen canvas
3. p5.js script:
   - L-system setup with axiom and rules
   - String generation through iterations
   - Turtle graphics interpretation of the L-system string
   - Wind effect using frameCount and sin()

I'll use a classic tree-like L-system:
- Axiom: "F"
- Rule: F -> FF+[+F-F-F]-[-F+F+F] or something similar that creates branching
- Angle: around 25 degrees
- Recursive depth: 4-5 iterations

For the wind effect, I'll modulate the rotation angle based on:
- Depth in the tree (branches sway less or more depending on level)
- Time (sin wave)
- Possibly some noise for irregularity

Let me write the code.

The code is complete. Let me verify it's a valid L-system implementation:

1. Uses p5.min.js locally - ✓
2. Self-contained single HTML file - ✓
3. L-system with axiom "F" and rule that creates branching - ✓
4. Turtle graphics interpretation using F, +, -, [, ] - ✓
5. Wind effect using sin() based on frameCount and depth - ✓
6. Gradual color change from brown to green - ✓
7. Background with stars - ✓

The implementation looks correct. The wind calculation uses multiple sine waves for organic movement, and depth-based wind influence makes outer branches sway more than the trunk.