fix issue where shipyard did not produce anything

docs/requirements.md

@@ -68,7 +68,7 @@ Output port indicators are not building tiles themselves. A building may have mo
 - REQ-BLD-SMELTER: **Smelter** (2×2): Converts ore or scrap into basic materials. No recipe selection required. Inputs, outputs, and rates are defined in `recipes.toml [[recipe]]` entries with `building = "smelter"`.
 - REQ-BLD-ASSEMBLER: **Assembler** (3×3): The player selects a recipe from the config-defined crafting tree. Produces the selected output item at the rate defined in the corresponding `recipes.toml [[recipe]]` entry with `building = "assembler"`.
 - REQ-BLD-REPROCESSING: **Reprocessing Plant** (3×3): Consumes scrap per cycle and produces exactly one higher-level intermediate product per cycle via weighted random pick. The input quantity, possible output items, per-output weights, and amounts are defined in `recipes.toml [[recipe]]` entries with `building = "reprocessing_plant"` (`inputs`, `outputs[].item`, `outputs[].amount`, `outputs[].weight`). Weights are normalized at load time; their sum does not need to equal 1. The output is rolled at cycle start (see REQ-MAT-CYCLE). The output buffer holds at most one cycle's output — see REQ-MAT-OUTPUT-BUFFER-REPROCESSING.
-- REQ-BLD-SHIPYARD: **Shipyard** (4×2): The player selects a blueprint. Automatically produces one ship of that type at `ships.toml [ship.blueprint].player_production_level` (initial value 5, incremented by duplicate blueprint drops per REQ-DEF-BLUEPRINT-DROP) whenever all required materials (`[ship.blueprint].materials`) are present in its input buffer.
+- REQ-BLD-SHIPYARD: **Shipyard** (4×2): The player selects a blueprint. When all required materials (`[ship.blueprint].materials`) are present in its input buffer, the shipyard consumes them and begins a production cycle lasting `[ship.blueprint].production_time_seconds` seconds (read from `ships.toml`). One ship of that type is spawned at `ships.toml [ship.blueprint].player_production_level` (initial value 5, incremented by duplicate blueprint drops per REQ-DEF-BLUEPRINT-DROP) when the cycle completes. The shipyard cannot start a new cycle while one is in progress.
 - REQ-BLD-SALVAGE-BAY: **Salvage Bay** (3×2): A dedicated drop-off point for salvage ships. Scrap delivered here is placed onto connected output belts.
 - REQ-BLD-BELT: **Belt** (1×1): Transports items. A belt tile has one direction (N, S, E, W) set at placement (modified by rotation). Curved belts are auto-derived: when a belt tile's outgoing direction leads into another belt whose direction is orthogonal, the downstream belt is rendered and behaves as a curve. Belt speed is defined in `world.toml [world].belt_speed_tiles_per_second` (REQ-GW-BELT-SPEED).
 - REQ-BLD-SPLITTER: **Splitter** (1×1): Distributes incoming items between two output directions. Each output can optionally have a filter (a list of item types), configurable via the selected building panel. Routing rules: