fix(ui): F8-06 calculator polish — always 3-decimal display, mono font, input cap

Owner feedback round 2 on PR #61:

- Pad every read-only calculator value to three decimals: tech labels,
  derived results (mass, speed, attack, defence, bombing, cargo
  capacity), planet MAT, planet build-rate, modernization cost, and
  the full-cargo capacity label all read as "1.000" instead of "1",
  matching the goal-seek back-solved input and the report. Drops
  thousands grouping so the same `fmt()` string also embeds cleanly
  in the read-only `<input type="number">` cell.
- Switch label and input styling onto the existing `--font-mono`
  token (right-aligned, tabular-nums) so columns line up vertically
  across rows like a financial table.
- Refuse a fourth decimal as the user types in every calculator
  number input (DWSC blocks, tech, MAT, custom load, lock value,
  modernization target tech): the `oninput` truncates the input text
  past three decimal digits and explicitly writes the truncated
  value back through `bind:value`, so Svelte's later reactive flush
  cannot undo the cap.
- Doc + tests follow the rule (five new vitest cases covering the
  3-decimal label format, the input cap on each input class, and
  the integer-padding rule for derived results).

ui/docs/calculator-ux.md

@@ -111,13 +111,19 @@ negative, the five blocks follow the engine value rules
 (`pkg/calc/validator.go`, surfaced per-field by
 `shipClassFieldErrors`), and a custom load may not exceed cargo capacity.
 
-Every displayed number — the derived results and the goal-seek
-back-solved input — is rounded **up** to three decimals through the
-shared `pkg/calc/number.go.Ceil3` (bridged as `core.ceil3`), so a value
-is never shown lower than it is (a speed of 5.0003 reads 5.001). The
-engine keeps its own round-to-nearest `util.Fixed*`; `Ceil3` is a
-display-only helper that lives in `pkg/calc` so the UI and Go share one
-implementation.
+Every displayed number — the derived results, the inherited tech /
+planet MAT labels, and the goal-seek back-solved input — is rounded
+**up** to three decimals through the shared `pkg/calc/number.go.Ceil3`
+(bridged as `core.ceil3`) and always padded to three decimals so the
+column reads the same on integers and fractions alike (a speed of 20
+shows as `20.000`, of 5.0003 as `5.001`). Labels and inputs use the
+monospace stack from the design tokens (`--font-mono`) with
+right-aligned, tabular numerals so values line up vertically across
+rows. To match the display rule, every number input also refuses a
+fourth decimal as the user types: typing `1.2345` clamps the input to
+`1.234` on input. The engine keeps its own round-to-nearest
+`util.Fixed*`; `Ceil3` is a display-only helper that lives in `pkg/calc`
+so the UI and Go share one implementation.
 
 ## Create / load / delete