ui/phase-18: ship-class calc bridge with live designer preview

Wires pkg/calc/ship.go into the WASM Core boundary as seven thin
wrappers (DriveEffective, EmptyMass, WeaponsBlockMass, FullMass,
Speed, CargoCapacity, CarryingMass). The ship-class designer reads
Core through a new CORE_CONTEXT_KEY populated by the in-game layout
and renders a five-row preview pane (mass, full-load mass, max
speed, range at full load, cargo capacity) that updates reactively
on every form edit and on the player's localPlayer{Drive,Weapons,
Shields,Cargo} tech levels — three of which are now decoded from
the report's Player block alongside the existing localPlayerDrive.

CarryingMass is the seventh wrapper added to the original six-function
list so that "full-load mass" composes through pkg/calc/ functions
without putting math in TypeScript.

ui/core/README.md

@@ -39,6 +39,8 @@ parity and round-trip sign/verify are exercised by
 ```text
 ui/core/
 ├── go.mod               module galaxy/core (Go 1.26.0)
+├── calc/                ship-math wrappers over `pkg/calc/ship.go`
+│   └── ship.go          Phase 18 designer preview bridge
 ├── canon/               canonical-bytes builders and verifiers
 │   ├── canon.go         length-prefix helpers
 │   ├── request.go       galaxy-request-v1 fields and signing input
@@ -88,6 +90,23 @@ ui/core/
 - Sentinel errors: `ErrInvalidPrivateKey`, `ErrInvalidPublicKey`,
   `ErrInvalidPublicKeyEncoding`.
 
+### `galaxy/core/calc`
+
+Thin Go bridge over `pkg/calc/ship.go`, surfaced via WASM to the
+Phase 18 ship-class designer preview. Each function is a one-line
+passthrough — no math lives here.
+
+- `DriveEffective(drive, driveTech float64) float64`
+- `EmptyMass(drive, weapons float64, armament uint, shields, cargo float64) (float64, bool)`
+- `WeaponsBlockMass(weapons float64, armament uint) (float64, bool)`
+- `FullMass(emptyMass, carryingMass float64) float64`
+- `Speed(driveEffective, fullMass float64) float64`
+- `CargoCapacity(cargo, cargoTech float64) float64`
+- `CarryingMass(load, cargoTech float64) float64`
+
+The full audit trail (which UI feature uses what, what is still
+deferred) lives in [`ui/docs/calc-bridge.md`](../docs/calc-bridge.md).
+
 ### `galaxy/core/types`
 
 - `RequestEnvelope`, `ResponseEnvelope`, `EventEnvelope` — full Go