fix(ui): calculator polish — smart input steps, unified tech/MAT lock idiom, tech floor, speed-lock ceiling fix

- pkg/calc: DriveForSpeed treats restMass==0 as a valid ceiling-only
  case (every positive drive solves it), so locking the displayed
  speed of a D=1, W=A=S=C=0 ship is no longer a phantom "infeasible".
- ship-design-area: drive/weapons/shields/cargo inputs use a JS-driven
  smart step on ArrowUp/ArrowDown (0↔1 jump, otherwise ±0.1) and hide
  the native spinner so it cannot produce invalid (0, 1) values;
  armament keeps its native step 1.
- Tech and planet MAT cells follow the same lock idiom as goal-seek
  locks: open padlock (🔓) over the inherited value → click to open
  an input with a closed padlock (🔒). The padlock slot is always
  reserved, so the column width is stable.
- Tech overrides (design area and modernization target) are floored
  at the player's current tech on this turn — a lower value is
  flagged as invalid.

ui/frontend/src/lib/i18n/locales/en.ts

@@ -393,7 +393,9 @@ const en = {
 	"game.calculator.lock.reset": "locked — click to release to the computed value",
 	"game.calculator.lock.infeasible": "this target cannot be reached with the current design",
 	"game.calculator.lock.max": "release the locked result first — one result at a time",
+	"game.calculator.tech.override": "click to override your current tech",
 	"game.calculator.tech.reset": "overridden — click to reset to your current tech",
+	"game.calculator.mat.override": "click to override the planet value",
 	"game.calculator.mat.reset": "overridden — click to reset to the planet value",
 	"game.calculator.modern.current": "current",
 	"game.calculator.modern.target": "target",
@@ -418,6 +420,7 @@ const en = {
 	"game.calculator.invalid.all_zero": "at least one value must be nonzero",
 	"game.calculator.invalid.negative": "value cannot be negative",
 	"game.calculator.invalid.tech_value": "tech level cannot be negative",
+	"game.calculator.invalid.tech_below_current": "tech level cannot be below your current tech this turn",
 	"game.calculator.invalid.load_over_capacity": "load exceeds the ship's cargo capacity",
 	"game.calculator.lock.no_drive": "set a non-zero drive before locking speed",