fix(test): add missing fields to stale struct literals across workspace tests

Four E0063 compile errors broke `cargo test --workspace --no-run`, blocking
`./run dist:test` on the DO fleet. Each is a stale struct literal in test/test-cfg
code that drifted from its current definition:

- mc-worldsim event_dispatch low_bio_thresholds: BiologicalThresholds missing
  migration_drought_factor / migration_drought_max (p3-21 drought coupling) —
  set to 0.0 / 1.0 to keep the helper's migration-suppression intent.
- mc-mod-host wasm_controller_{noop,limits}: TacticalState missing embark_level —
  Default::default() (EmbarkLevel::None) to match the empty-state intent.
- api-gdext ai.rs tile_with + ai_controller test: TacticalTile missing explored /
  TacticalState missing embark_level — explored:true (pre-field default = seen),
  embark_level default.

Mirrors the sibling fix 04fabbc1c. `cargo test --workspace --no-run` now compiles
clean; full suite passes except 3 pre-existing GPU-parity tests (Metal fp drift,
unrelated to these changes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/simulator/api-gdext/src/ai.rs

@@ -1075,6 +1075,7 @@ mod tests {
             resource: None,
             is_coast: false,
             owner: None,
+            explored: true,
         }
     }
 

src/simulator/api-gdext/tests/ai_controller.rs

@@ -79,6 +79,7 @@ fn minimal_tactical_state_json_parses() {
         unit_catalog: Vec::new(),
         building_catalog: Vec::new(),
         difficulty_threshold_mult: 1.0,
+        embark_level: Default::default(),
     };
     let json = serde_json::to_string(&minimal).expect("serialize");
     let parsed = parse_tactical_state_json(&json).expect("parse");

src/simulator/crates/mc-mod-host/tests/wasm_controller_limits.rs

@@ -31,6 +31,7 @@ fn empty_state() -> TacticalState {
         unit_catalog: Vec::new(),
         building_catalog: Vec::new(),
         difficulty_threshold_mult: 1.0,
+        embark_level: Default::default(),
     }
 }
 

src/simulator/crates/mc-mod-host/tests/wasm_controller_noop.rs

@@ -23,6 +23,7 @@ fn empty_state() -> TacticalState {
         unit_catalog: Vec::new(),
         building_catalog: Vec::new(),
         difficulty_threshold_mult: 1.0,
+        embark_level: Default::default(),
     }
 }
 

src/simulator/crates/mc-worldsim/src/event_dispatch.rs

@@ -322,6 +322,8 @@ mod tests {
             migration_differential_min: 3.0,
             migration_trigger_chance: 1.0,
             migration_max_hops: 3,
+            migration_drought_factor: 0.0, // disable drought coupling in this helper
+            migration_drought_max: 1.0,
         }
     }