DOC: add aerodynamic surfaces user guide

[ViniciusCMB]

Summary:
Add comprehensive user guide documentation for aerodynamic surfaces in RocketPy.

Changes:

• New file: docs/user/aerodynamics/surfaces.rst — Complete user guide covering nose cones, fins, tails, and generic surfaces
• Modified: docs/user/index.rst — Added "Aerodynamic Surfaces" to the "Further Analysis" section

What the documentation covers:
Nose Cones

• 8 supported kinds: conical, ogive, elliptical, tangent, von karman, parabolic, powerseries, lvhaack
• Geometric parameters (length, base_radius, position)
• Parameter-specific notes (bluffness for ogive, power for powerseries)

Fins

• Three geometries: Trapezoidal, Elliptical, Free Form
• Distinction between fin sets (TrapezoidalFins, EllipticalFins, FreeFormFins) and individual fins (TrapezoidalFin, EllipticalFin, FreeFormFin)
• Geometric parameters for each type
• Airfoil profile support (CSV format, units)
• Complete code example using rocket.add_trapezoidal_fins()

Tail

• Parameters: top_radius, bottom_radius, length, position

Generic Surfaces

• Overview of GenericSurface and LinearGenericSurface for custom aerodynamic coefficients
• Use cases: CFD/wind tunnel data, non-standard surfaces (canards, air brakes)
• Cross-reference to detailed generic surface guide

Reference Area & Length

• Explanation of reference area (πr²) and reference length (2r)

Cross-references:

• Links to technical docs: Individual Fin Model, Elliptical Fins Equations, Roll Equations
• Links to coordinate system docs: Rocket Class Axes Definitions, Positions and Coordinate Systems

Pull request type:

• ReadMe, Docs and GitHub updates

Checklist:

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md has been updated (if relevant)

Current behavior:
No dedicated user guide for aerodynamic surfaces existed. Users had to piece together information from class docstrings, technical docs, and examples.

New behavior:
A new comprehensive user guide page (docs/user/aerodynamics/surfaces.rst) provides:

• Overview of all aerodynamic surface types (nose cones, fins, tails, generic surfaces)
• Geometric parameters for each surface kind
• Code examples for adding surfaces to a rocket
• Airfoil profile documentation
• Distinction between fin sets and individual fins (new in Individual Fins feature)
• Cross-references to technical derivations and coordinate system docs

The page is linked from the user guide index under "Further Analysis".

Breaking change:
No

Additional information:
This documentation supports the Individual Fins feature (PR #818) by clearly documenting the difference between fin set classes and individual fin classes, their respective use cases, and when to use each approach.

[Gui-FernandesBR]

LGTM

can you also add your PR to the CHANGELOG please?