Add charging bow visualization for long touch

[wannerdev]

Description

Adds a visual charging effect that appears behind Earth when holding touch on mobile, showing the force magnitude building up like drawing a bow.

Changes

• Created new charging_bow module in effects
• Implemented draw_charging_bow system
• Shows expanding arc behind Earth as touch is held
• Arc grows from 8.0 to 14.0 radius over 1 second (matches force cap)
• Color transitions from orange to bright yellow as it charges
• Pulsing energy particles at bow tips when fully charged (>90%)
• Multiple arc layers for depth effect
• Integrated into effects plugin system

Visual Effect Details

• Trigger: When LaunchArmed is true and touch is being held
• Position: Behind Earth (180-degree arc)
• Radius: Grows from 8.0 to 14.0 based on charge (0-100%)
• Color: Orange (1.0, 0.4, 0.0) → Yellow (1.0, 1.0, 0.0)
• Alpha: Increases from 0.6 to 1.0 as it charges
• Duration: Matches 1-second force cap from game mechanics
• Particles: Pulsing yellow circles at bow tips when >90% charged

Charging Mechanics

• 0-5% charge: No visual (prevents flicker)
• 5-90% charge: Growing orange-to-yellow arc
• 90-100% charge: Full arc + pulsing energy particles
• Release: Effect disappears instantly on launch

Bow Design

• Shape: 180-degree arc behind Earth (semicircle)
• Layers: 3 concentric arcs for thickness effect
• Segments: 20 line segments per arc for smooth curve
• Transparency: Outer arcs more transparent for depth
• Particles: 2 pulsing circles at arc endpoints when charged

Benefits

• Provides clear visual feedback for force charging
• Helps mobile users understand hold-to-charge mechanic
• Shows exactly how much force will be applied
• Makes launch power predictable and controllable
• Enhances mobile UX with intuitive visual language
• Adds satisfying visual feedback for charging
• Matches bow-and-arrow metaphor for launching

Technical Implementation

• Queries LaunchArmed to check if earth is selected
• Uses LaunchState.launched_at_time to calculate hold duration
• Calculates charge percentage (0.0 to 1.0) capped at 1 second
• Draws arc using multiple line segments in semicircle
• Color interpolation based on charge percentage
• Particle pulse uses sine wave animation
• Uses gizmos for efficient rendering

Force Visualization

• Visual charge directly corresponds to actual launch force
• Game caps force at 1 second hold time
• Bow visualization matches this 1-second cap
• Players can see exactly how much force they're applying
• Helps with precision launches and orbital mechanics

Performance

• Lightweight: Only draws when charging
• Efficient: Uses gizmos (no sprites/meshes)
• Minimal: ~60 line segments + 2 circles when fully charged
• Real-time: Updates every frame for smooth animation
• Clean: No entity spawning (pure rendering)

Testing

• Tap and hold Earth on mobile device
• Verify orange arc appears behind Earth
• Hold longer and verify arc grows and turns yellow
• Hold for 1 second and verify pulsing particles appear
• Release and verify arc disappears
• Check that arc size correlates with launch force
• Test that color transition is smooth

Related Issue

Fixes: Android/Mobile Feedback - When touching longer this force needs symbolising, a charging bend of a bow behind earth (mobile)