allow one target per repair tool module

docs/requirements.md

@@ -166,6 +166,8 @@ Modules in `modules.toml` define a `surface_mask` — a list of strings that des
   Each salvage module instance operates independently: it has its own cargo hold (`cargo_capacity`), collection range (`collection_range`), and collection rate (`collection_rate`, in collections per second). After collecting a piece of scrap, the module cannot collect again until `1 / collection_rate` seconds have elapsed. A ship with multiple salvage modules can therefore collect multiple pieces of scrap per tick (one per ready module), and installs of different module types may have different ranges and rates. The ship navigates based on the maximum collection range across all installed salvage modules.
 - REQ-SHP-REPAIR: Ships with at least one **repair module** (player) — patrol by moving forward (rightward, away from the asteroid) while searching sensor range. If a damaged player defence station or player ship enters sensor range, move to it and repair. If an enemy ship enters sensor range while not currently repairing, turn back (move toward the asteroid) until the enemy is no longer in sensor range, then resume patrol. The player can configure the target priority per shipyard:
   - Defence stations first / ships first / nearest target.
+
+  Each repair module instance operates independently: it has its own repair rate (`repair_rate`) and repair range (`repair_range`). On each tick, a module first attempts to heal the ship's current behavior-level navigation target if that target is within the module's `repair_range` and is damaged (HP above zero and below maximum HP). If those conditions are not met — because the target is out of the module's `repair_range`, already at full health, or destroyed — the module independently searches for the nearest damaged friendly (player ship or player defence station) within its own `repair_range` and heals that instead. If no valid target is found within range, the module idles. A ship with multiple repair modules can therefore heal different targets simultaneously. Navigation is driven solely by the behavior-level target; individual module fallback targets do not affect which direction the ship moves.
 - REQ-SHP-ENEMY-AI: **Enemy ships** — engage the closest valid target (player defence station, HQ, or player ship) within their sensor range. If no target is in sensor range, they move toward the asteroid (leftward in world coordinates).
 - REQ-SHP-SCHEMATICS: The player selects a schematic per shipyard by clicking it. New schematics are unlocked automatically when an enemy defence station set is destroyed (REQ-DEF-SCHEMATIC-DROP) — there is no physical loot to collect.