change to physics based ship movement

docs/requirements.md

@@ -7,7 +7,7 @@ Config files use the TOML format. The following config files drive game paramete
 - **world.toml** — world dimensions, region widths, expansion amounts, building refund percentage, wave timing, enemy ship level formula, belt speed, starting building blocks, departure interval.
 - **buildings.toml** — building block cost and construction time per building type.
 - **recipes.toml** — crafting recipes: inputs, outputs, quantities, durations, and reprocessing plant probabilities.
-- **ships.toml** — per schematic: a human-readable display name (used in toasts and UI), ship stats (HP, speed, damage, attack range, attack rate, sensor range) as formulas of ship level, required build materials, threat cost formula, player production level, whether the schematic is available from game start, and a layout grid defining the ship's module slots.
+- **ships.toml** — per schematic: a human-readable display name (used in toasts and UI), ship stats (HP, max linear speed, damage, attack range, attack rate, sensor range, main acceleration, maneuvering acceleration, angular acceleration, max rotation speed) as formulas of ship level, required build materials, threat cost formula, player production level, whether the schematic is available from game start, and a layout grid defining the ship's module slots.
 - **modules.toml** — per module type: id, surface mask, materials list, player production level, production time, threat cost, fill color, glyph, and stat modifier formulas (additive and/or multiplicative per stat).
 - **stations.toml** — HP, damage, range, fire rate, and scrap drop for player and enemy defence stations, defined as formulas of station level.
 - **visuals.toml** — rendering-only config (not game parameters): fill and outline colors and glyphs for every building type, item type, ship role, and station type; beam color and width; overlay and toast colors. Loaded by the UI at startup; the simulation does not read it.
@@ -149,10 +149,10 @@ Modules in `modules.toml` define a `surface_mask` — a list of strings that des
 ## Ships
 
 - REQ-SHP-AUTONOMOUS: Ships are produced by shipyards and are fully autonomous once produced.
-- REQ-SHP-STATS: Base ship stats are defined as formulas of ship level in `ships.toml`: HP (`[ship.health].hp_formula`), speed (`[ship.movement].speed_formula`), damage (`[ship.combat].damage_formula`), attack range (`[ship.combat].attack_range_formula`), attack rate (`[ship.combat].attack_rate_formula`), sensor range (`[ship.sensors].range_formula`). Required build materials (`[ship.schematic].materials`) and availability from game start (`[[ship]].available_from_start`) are also defined there. Final ship stats incorporate module modifiers per REQ-MOD-STAT-CALC.
+- REQ-SHP-STATS: Base ship stats are defined as formulas of ship level in `ships.toml`: HP (`[ship.health].hp_formula`), max linear speed (`[ship.movement].speed_formula`), damage (`[ship.combat].damage_formula`), attack range (`[ship.combat].attack_range_formula`), attack rate (`[ship.combat].attack_rate_formula`), sensor range (`[ship.sensors].range_formula`), main acceleration (`[ship.movement].main_acceleration_formula`, tiles/s²), maneuvering acceleration (`[ship.movement].maneuvering_acceleration_formula`, tiles/s²), angular acceleration (`[ship.movement].angular_acceleration_formula`, rad/s²), max rotation speed (`[ship.movement].max_rotation_speed_formula`, rad/s). Required build materials (`[ship.schematic].materials`) and availability from game start (`[[ship]].available_from_start`) are also defined there. Final ship stats incorporate module modifiers per REQ-MOD-STAT-CALC.
 - REQ-SHP-SPAWN-PLAYER: A ship produced by a shipyard spawns centered on the shipyard's output port tile.
 - REQ-SHP-SPAWN-ENEMY: Enemy ships spawn at a uniformly random position within the current enemy buffer zone — random X across the buffer's width and random Y across the world height.
-- REQ-SHP-MOVEMENT: Ships move in straight lines toward their current destination at the speed defined by their speed formula. Ship position refers to the ship's center for all range, sensor, and attack checks.
+- REQ-SHP-MOVEMENT: Ships move using a physics-based model. Each ship has a velocity and a facing direction, both updated each tick. The main acceleration (`main_acceleration_formula`) is applied along the ship's current facing direction only. The maneuvering acceleration (`maneuvering_acceleration_formula`) can be applied in any direction independently of the facing direction, enabling lateral or braking movement without rotating. The angular acceleration (`angular_acceleration_formula`) controls how quickly the ship rotates. Linear speed is capped at the ship's `speed_formula` value; rotation rate is capped at the ship's `max_rotation_speed_formula` value. Ship position refers to the ship's center for all range, sensor, and attack checks.
 - REQ-SHP-NO-COLLISION: Ships do not collide with each other or with defence stations; they may visually overlap.
 - REQ-SHP-SENSOR: A ship perceives only entities within its sensor range. Behavior is driven by what is in sensor range; entities outside sensor range are ignored.
 - REQ-SHP-FIRING: All weapons — on ships and on defence stations — fire when off cooldown and the target is within attack range. Firing emits a fire event and starts a 0.15-second damage delay (half the beam duration). When that delay expires, damage is applied to the target — unless the target has already been destroyed, in which case the damage is silently dropped. If the shooter is destroyed before the delay expires, damage is still applied when the delay expires. There is no projectile entity and no intervening collision. The weapon's cooldown begins at the moment of firing, not at damage application.