Replace random vehicle spawning with deterministic Berlin ring route

[Copilot]

Replaces random vehicle scatter with a fixed Berlin S-Bahn Ringbahn pattern to enable visual validation of the data pipeline.

Changes

• routes.rs: New module with berlin_ring_route() returning 15 waypoints forming a ring around central Berlin using real Ringbahn coordinates
• main.rs: Modified spawn_vehicles() to distribute all 5,000 vehicles evenly along the shared route with ±0.0001° jitter, uniform 0.0008 speed, and sequential waypoint assignment
• movement.rs: Tightened WAYPOINT_THRESHOLD from 0.0005 to 0.0002 for precise route following

Result

All vehicles now form a visible ring and move in a train pattern, creating a deterministic visual signature through the entire pipeline (Simulator → Kafka → Ingest → Redis → WebSocket → React).

// Before: Random scatter with individual square routes
let start_pos = Vec2::new(
    CENTER.x + rng.gen_range(-SPREAD..SPREAD),
    CENTER.y + rng.gen_range(-SPREAD..SPREAD),
);

// After: Distributed along shared Berlin ring
let waypoint_index = i % num_waypoints;
let base_pos = waypoints[waypoint_index];
let start_pos = base_pos + Vec2::new(rng.gen_range(-0.0001..0.0001), ...);

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Original prompt

Visual Validation Feature: Berlin Ring Route

Objective

Replace the current vehicle spawning logic with a deterministic Berlin ring route pattern for visual pipeline validation.

Changes Required

1. Create crates/traffic-sim/src/routes.rs:

   • Add a function berlin_ring_route() that returns a Vec of Vec2 waypoints
   • Use real S-Bahn Ringbahn coordinates around central Berlin (approximately 15 waypoints forming a ring)
   • Coordinates should form a recognizable circular pattern around Berlin center

2. Update crates/traffic-sim/src/main.rs:

   • Add mod routes; declaration at the top with other modules
   • Add use routes::berlin_ring_route; import
   • Replace the spawn_grid_vehicles function with spawn_vehicles function that:
     • Takes the Berlin ring route waypoints
     • Distributes all vehicles evenly along the route (using modulo to cycle through waypoints)
     • Adds small random offset (±0.0001°) to each vehicle to avoid perfect overlap
     • Sets all vehicles to similar speed (0.0008) for clear visualization
     • Uses the shared ring route for all vehicles
     • Each vehicle's current_waypoint should be set to the next waypoint in sequence
   • Update the call in main() from spawn_grid_vehicles(&mut world, 3000) to spawn_vehicles(&mut world, 5000)

3. Update crates/traffic-sim/src/systems/movement.rs:

   • Change WAYPOINT_THRESHOLD from 0.0005 to 0.0002 for tighter route following

Expected Result

• All 5,000 vehicles forming a clear visible ring around central Berlin
• Vehicles moving in a "train" pattern around the circle
• Ring aligns with real Berlin streets (S-Bahn Ringbahn approximation)
• No random scatter - deterministic, reproducible pattern

Implementation Details

The Berlin ring route should include waypoints like:

• Westkreuz: 13.3884, 52.5244
• Südkreuz area: 13.3650, 52.4750
• Ostkreuz area: 13.5030, 52.4650
• Prenzlauer Berg: 13.5050, 52.5400
• Wedding: 13.4500, 52.5650
• And approximately 10 more points forming a complete ring

This creates a visual sanity check for the entire data pipeline (Rust Simulator → Kafka → Ingest → Redis → WebSocket → React).

This pull request was created as a result of the following prompt from Copilot chat.

Visual Validation Feature: Berlin Ring Route

Objective

Replace the current vehicle spawning logic with a deterministic Berlin ring route pattern for visual pipeline validation.

Changes Required

1. Create crates/traffic-sim/src/routes.rs:

   • Add a function berlin_ring_route() that returns a Vec of Vec2 waypoints
   • Use real S-Bahn Ringbahn coordinates around central Berlin (approximately 15 waypoints forming a ring)
   • Coordinates should form a recognizable circular pattern around Berlin center

2. Update crates/traffic-sim/src/main.rs:

   • Add mod routes; declaration at the top with other modules
   • Add use routes::berlin_ring_route; import
   • Replace the spawn_grid_vehicles function with spawn_vehicles function that:
     • Takes the Berlin ring route waypoints
     • Distributes all vehicles evenly along the route (using modulo to cycle through waypoints)
     • Adds small random offset (±0.0001°) to each vehicle to avoid perfect overlap
     • Sets all vehicles to similar speed (0.0008) for clear visualization
     • Uses the shared ring route for all vehicles
     • Each vehicle's current_waypoint should be set to the next waypoint in sequence
   • Update the call in main() from spawn_grid_vehicles(&mut world, 3000) to spawn_vehicles(&mut world, 5000)

3. Update crates/traffic-sim/src/systems/movement.rs:

   • Change WAYPOINT_THRESHOLD from 0.0005 to 0.0002 for tighter route following

Expected Result

• All 5,000 vehicles forming a clear visible ring around central Berlin
• Vehicles moving in a "train" pattern around the circle
• Ring aligns with real Berlin streets (S-Bahn Ringbahn approximation)
• No random scatter - deterministic, reproducible pattern

Implementation Details

The Berlin ring route should include waypoints like:

• Westkreuz: 13.3884, 52.5244
• Südkreuz area: 13.3650, 52.4750
• Ostkreuz area: 13.5030, 52.4650
• Prenzlauer Berg: 13.5050, 52.5400
• Wedding: 13.4500, 52.5650
• And approximately 10 more points forming a complete ring

This creates a visual sanity check for the entire data pipeline (Rust Simulator → Kafka → Ingest → Redis → WebSocket → React).

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