Assemble a body's readouts once, not once per panel

Follow-up to review on #3. The card and the detail page each built their own Measured/Derived
split, kind label and provenance sentence — the drift buildBodyViewModel exists to prevent,
re-forked one layer up, and the drift would have been in which side of the measured/derived line
a quantity falls on, which is the distinction those panels exist to draw. One bodyReadouts(body)
now returns both blocks and the sentence, and both templates iterate it. The two surfaces render
identical rows as a result, and the card gains the inclination the detail page already showed.

Also from that review:

- KIND_LABELS was duplicated between the two panels; it now lives beside bodyReadouts. The third
  copy the review pointed at is a different union (search results are star/body/exoplanet, and
  label a body "Body"), so it stays where it is.
- CardRow was HudReadout renamed. Both are now Readout, which HudReadout extends with its
  derived flag.
- The enterable-systems count was a 21-line lazy memo over arrays that are already in hand; it is
  one expression where those arrays are assigned.
- buildBodyViewModel now carries hostStarId, so the detail scene stops rescanning both catalogues
  for something the builder had already resolved.
- heliocentricPeriodDays was called twice for the same body.
- The superscript helper was a split/map/join; it is a replace.
- info-panel had five computed() each wrapping one pure call with a non-null assertion, beside a
  template that inlined the same kind of call directly. They are gone with the shared readouts.
- Dropped a tautological test that compared a pure function to itself. Replaced with one that
  asserts the host star id the builder now carries.
- Removed the orphaned doc comment left behind when formatParsecs/formatAu moved out.

And one the review raised as out of scope but is worth taking: formatRadiusKm grouped thousands
above its decimal threshold and not below it, so 69,911 km sat beside a bare 6371 km. Both are
grouped now.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaySiNst4HhDXBHnMy8p5G

src/app/features/body-detail/body-readouts.ts

@@ -0,0 +1,82 @@
+import { PLANET_CLASS_LABELS } from '../../shared/astro/planet-appearance';
+import { formatAu, formatDensity, formatMassEarth, formatPeriod, formatRadiusKm, formatTemperature } from '../../shared/format/quantity';
+import { Readout } from '../../shared/models/readout';
+import { BodyDetailViewModel } from './body-detail.model';
+
+export const KIND_LABELS: Readonly<Record<BodyDetailViewModel['kind'], string>> = {
+  planet: 'Planet',
+  moon: 'Moon',
+  dwarf: 'Dwarf planet',
+  exoplanet: 'Exoplanet'
+};
+
+export interface BodyReadouts {
+  readonly kindLabel: string;
+  /** Only what a catalogue actually published for this body. */
+  readonly measured: readonly Readout[];
+  /** Everything computed from those measurements rather than observed directly. */
+  readonly derived: readonly Readout[];
+  /** Says plainly which of the two the surface being drawn is. */
+  readonly provenance: string;
+}
+
+/**
+ * Turns a body into the rows its panels display.
+ *
+ * Shared by the in-map card and the detail page for the same reason `buildBodyViewModel` is:
+ * two independent assemblies of "what do we know about this world" drift, and here the drift
+ * would be in which side of the measured/derived line a quantity falls on — which is the one
+ * distinction these panels exist to make.
+ */
+export function bodyReadouts(body: BodyDetailViewModel): BodyReadouts {
+  const measured: Readout[] = [];
+  if (body.radiusKm !== undefined) {
+    measured.push({ label: 'Radius', value: formatRadiusKm(body.radiusKm) });
+  }
+  if (body.massEarth !== undefined) {
+    measured.push({ label: 'Mass', value: formatMassEarth(body.massEarth) });
+  }
+  if (body.orbit.semiMajorAxisAu !== undefined) {
+    measured.push({ label: 'Semi-major axis', value: formatAu(body.orbit.semiMajorAxisAu) });
+  }
+  if (body.orbit.eccentricity !== undefined) {
+    measured.push({ label: 'Eccentricity', value: body.orbit.eccentricity.toFixed(3) });
+  }
+  if (body.orbit.inclinationDeg !== undefined) {
+    measured.push({ label: 'Inclination', value: `${body.orbit.inclinationDeg.toFixed(2)}°` });
+  }
+  // The period sits under whichever heading its provenance calls for. Same number, same field —
+  // a published period is an observation and a computed one is not.
+  if (body.orbitalPeriodDays !== undefined && body.orbitalPeriodSource === 'measured') {
+    measured.push({ label: 'Period', value: formatPeriod(body.orbitalPeriodDays) });
+  }
+  if (body.discoveryYear !== undefined) {
+    measured.push({ label: 'Discovered', value: `${body.discoveryYear}` });
+  }
+
+  const derived: Readout[] = [{ label: 'Class', value: PLANET_CLASS_LABELS[body.appearance.planetClass] }];
+  if (body.orbitalPeriodDays !== undefined && body.orbitalPeriodSource === 'derived') {
+    derived.push({ label: 'Period', value: formatPeriod(body.orbitalPeriodDays) });
+  }
+  if (body.appearance.equilibriumTemperatureK !== null) {
+    derived.push({ label: 'Equilibrium temp.', value: formatTemperature(body.appearance.equilibriumTemperatureK) });
+  }
+  if (body.appearance.bulkDensityGramsPerCm3 !== null) {
+    derived.push({ label: 'Bulk density', value: formatDensity(body.appearance.bulkDensityGramsPerCm3) });
+  }
+
+  return { kindLabel: KIND_LABELS[body.kind], measured, derived, provenance: provenanceFor(body) };
+}
+
+/**
+ * The derived surface is a reasoned illustration, and a panel of real measurements sitting next
+ * to it is exactly the context in which it could be mistaken for another one.
+ */
+function provenanceFor(body: BodyDetailViewModel): string {
+  if (body.hasPhotography) {
+    return 'Surface: NASA/ESA/USGS photography.';
+  }
+  return body.appearance.equilibriumTemperatureK === null
+    ? 'Surface illustrated from this body’s measured size and mass. Its host star is not in the catalogue, so no temperature could be derived. Not an observation — no image of this world exists.'
+    : 'Surface illustrated from the measurements above — size, density and the temperature derived from its star’s output and its orbit. Not an observation — no image of this world exists.';
+}