Implement config-driven unlock groups

Lift unlocking into first-class unlock groups defined in unlocks.toml, so
one defence-station drop can grant a bundle of ships/modules/buildings/
recipes at once (e.g. the salvager module + salvage bay), and buildings
can now be locked at game start and unlocked via a drop.

Config:
- New UnlocksConfig + ConfigLoader::loadUnlocks + validateUnlocks (unknown/
  duplicate/non-assembler grants, unknown requires, empty group all fail load).
- Drop unlock_at_station_level/unlock_requires from ship/module/recipe defs;
  add unlocked_at_start bool to recipes for graph-unreachable base recipes.

Simulation:
- Track awarded groups + per-building unlock state; an item starts unlocked
  iff no group grants it. Rework generateSchematicChoices/applySchematicChoice
  to operate on groups (grant all members at once). Extend state checksum.
- isBuildingUnlocked query; tryPlaceBuilding rejects locked types.

UI:
- Build-menu buttons for locked buildings start hidden, revealed via a new
  UnlockedBuildingsChangedEvent (emitted from GameWorldView's poll loop).
- Schematic choice dialog lists a group's granted items.
- Blueprint placement excludes locked building types (REQ-LOCK-UI-BLUEPRINT).

Data: unlocks.toml (app + test) reproduces the prior per-item gates as
singleton groups and adds salvage_operations (salvager + salvage_bay, lvl 1)
and reprocessing (reprocessing_plant, lvl 2).

Tests: rewrote unlock/config/recipe-schematic/artifact/wave/shipyard tests
for the group model; added UnlockGroupTest. All 443 cases pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7N59FsLA5e2kuVdqe4Uhc

src/lib/core/SchematicChoiceOption.h

@@ -3,23 +3,43 @@
 #include <string>
 #include <vector>
 
+// The kind of a single granted schematic within an unlock option.
 enum class SchematicType
 {
     Ship,
     Module,
-    Recipe,
-    Artifact
+    Building,
+    Recipe
+};
+
+// One item granted by an unlock group (REQ-LOCK-EXPLICIT), shown in the
+// schematic choice dialog's granted-items list.
+struct GrantedSchematic
+{
+    SchematicType type;
+    std::string id;
+    std::string displayName;
 };
 
 // One option presented to the player in the schematic choice dialog
 // (REQ-DEF-SCHEMATIC-DROP). Built by the simulation when enemy stations are
-// destroyed; the UI reads these to populate the dialog.
+// destroyed; the UI reads these to populate the dialog. A non-artifact option
+// represents one unlock group; selecting it awards the whole group.
 struct SchematicChoiceOption
 {
-    std::string schematicId;
-    SchematicType type;
+    bool isArtifact = false;
+
+    // Unlock group id (empty for the artifact option).
+    std::string unlockGroupId;
+
+    // Display name shown as the option's title: the unlock group's derived name,
+    // or "Artifact" for the artifact option.
     std::string displayName;
 
+    // The ships, modules, buildings, and assembler recipes this group grants
+    // (empty for the artifact option).
+    std::vector<GrantedSchematic> grantedItems;
+
     // Ids of miner/assembler recipes that would newly become implicitly
     // unlocked (REQ-LOCK-IMPLICIT) if this option is selected. Sorted
     // alphabetically by display name; empty if none.