chore: E6 polish wiki content (P1)

.github/wiki/examples/solar-position.md

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+# Example: Solar Position Logger
+
+Print solar position every 30 minutes throughout a day.
+
+```js
+import { calcSpa } from 'nrel-spa';
+
+const LAT = 40.7128;  // New York
+const LON = -74.0060;
+const TZ = -4;        // EDT
+
+const date = new Date('2025-06-21T00:00:00-04:00');
+
+console.log('Time (local)  Zenith    Azimuth');
+console.log('────────────  ────────  ────────');
+
+for (let hour = 4; hour <= 21; hour++) {
+  for (const min of [0, 30]) {
+    const d = new Date(date);
+    d.setHours(hour, min, 0, 0);
+    const r = calcSpa(d, LAT, LON, TZ);
+    const timeStr = `${String(hour).padStart(2, '0')}:${String(min).padStart(2, '0')}`;
+    const zenith = Number(r.zenith).toFixed(1).padStart(7);
+    const azimuth = Number(r.azimuth).toFixed(1).padStart(7);
+    console.log(`${timeStr}          ${zenith}°  ${azimuth}°`);
+  }
+}
+```
+
+Sample output (abbreviated):
+
+```
+Time (local)  Zenith    Azimuth
+────────────  ────────  ────────
+05:30           89.3°     60.2°
+06:00           83.1°     68.4°
+12:00           24.6°    185.1°
+13:00           26.1°    212.3°
+20:00           83.8°    293.7°
+```

.github/wiki/examples/twilight-times.md

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+# Example: Twilight Times
+
+Compute civil, nautical, and astronomical twilight for a location.
+
+```js
+import { getSpa, formatTime } from 'nrel-spa';
+
+const LAT = 34.0522;  // Los Angeles
+const LON = -118.2437;
+const TZ = -7;        // PDT
+
+const date = new Date('2025-09-15T12:00:00-07:00');
+
+const r = getSpa(date, LAT, LON, TZ, {}, [90.833, 96, 102, 108]);
+
+const labels = ['Sunrise/Sunset', 'Civil', 'Nautical', 'Astronomical'];
+
+for (let i = 0; i < r.customAngles.length; i++) {
+  const ca = r.customAngles[i];
+  const rise = formatTime(ca.sunrise);
+  const set  = formatTime(ca.sunset);
+  console.log(`${labels[i].padEnd(16)} dawn: ${rise}  dusk: ${set}`);
+}
+```
+
+Sample output:
+
+```
+Sunrise/Sunset   dawn: 06:30:42  dusk: 19:12:18
+Civil            dawn: 06:04:11  dusk: 19:38:49
+Nautical         dawn: 05:33:07  dusk: 20:09:53
+Astronomical     dawn: 05:01:19  dusk: 20:41:41
+```

.github/wiki/guides/advanced.md

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+# Advanced Usage
+
+## Twilight calculations
+
+Pass an array of custom zenith angles to compute additional rise/set events beyond the default solar disk (90.833°).
+
+```js
+import { getSpa } from 'nrel-spa';
+
+const result = getSpa(date, lat, lon, tz, {}, [96, 102, 108]);
+
+for (const ca of result.customAngles) {
+  const label = ca.angle === 96 ? 'Civil' : ca.angle === 102 ? 'Nautical' : 'Astronomical';
+  console.log(`${label} dawn: ${ca.sunrise.toFixed(4)} hours`);
+  console.log(`${label} dusk: ${ca.sunset.toFixed(4)} hours`);
+}
+```
+
+Zenith reference:
+- 90.833° — standard solar disk (default)
+- 96° — civil twilight
+- 102° — nautical twilight
+- 108° — astronomical twilight
+
+## Batch processing
+
+`getSpa` is synchronous, making batch work straightforward without async coordination.
+
+```js
+import { getSpa } from 'nrel-spa';
+
+const lat = 51.5074; // London
+const lon = -0.1278;
+const tz = 0;
+
+let totalDaylight = 0;
+for (let doy = 0; doy < 365; doy++) {
+  const d = new Date(Date.UTC(2025, 0, 1 + doy, 12, 0, 0));
+  const r = getSpa(d, lat, lon, tz);
+  if (isFinite(r.sunrise)) {
+    totalDaylight += r.sunset - r.sunrise;
+  }
+}
+console.log(`Annual daylight: ${totalDaylight.toFixed(0)} hours`);
+```
+
+## Polar scenarios
+
+At high latitudes, `sunrise` and `sunset` are `NaN` when the sun does not cross the horizon. Check with `isFinite()`.
+
+```js
+const r = getSpa(new Date('2025-12-21T12:00:00Z'), 89, 0, 0);
+console.log(isFinite(r.sunrise)); // false — polar night
+```
+
+`calcSpa` returns `"N/A"` strings in these cases.
+
+## vs solar-spa
+
+Both packages implement the same NREL SPA algorithm. Key differences:
+
+| | nrel-spa | solar-spa |
+|---|---|---|
+| Runtime | Pure JS | WebAssembly |
+| API | Synchronous | Async (Promise) |
+| Custom zenith | Yes | No |
+| Bundle size | ~38 KB | ~60 KB |
+| Init latency | None | First call |
+
+Use `nrel-spa` when you need synchronous calls or custom twilight angles. Use `solar-spa` when throughput for very large batches matters.
+
+## Delta-T
+
+The default `delta_t` is 67 seconds, accurate for dates near 2025. For historical dates or high-precision work, provide a value from the IERS or USNO tables.
+
+```js
+getSpa(new Date('1900-01-01T12:00:00Z'), lat, lon, tz, { delta_t: -2.72 });
+```

.github/wiki/guides/quickstart.md

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+# Quick Start
+
+Five minutes from install to solar position.
+
+## Install
+
+```sh
+npm install nrel-spa
+```
+
+## Basic usage
+
+```js
+import { getSpa } from 'nrel-spa';
+
+const result = getSpa(
+  new Date('2025-06-21T12:00:00Z'),
+  40.7128,   // latitude
+  -74.0060,  // longitude
+  -4,        // UTC offset in hours (EDT)
+);
+
+console.log(result.zenith);    // solar zenith angle in degrees
+console.log(result.azimuth);   // solar azimuth in degrees
+console.log(result.sunrise);   // fractional hours, e.g. 5.42
+console.log(result.sunset);    // fractional hours, e.g. 20.58
+console.log(result.solarNoon); // fractional hours, e.g. 13.00
+```
+
+`getSpa` is synchronous. There is no initialization step, no WASM loading, no async overhead.
+
+## Formatted output
+
+```js
+import { calcSpa } from 'nrel-spa';
+
+const result = calcSpa(
+  new Date('2025-06-21T12:00:00Z'),
+  40.7128,
+  -74.0060,
+  -4,
+);
+
+console.log(result.sunrise);    // "05:25:12"
+console.log(result.sunset);     // "20:34:47"
+console.log(result.solarNoon);  // "12:59:58"
+```
+
+## Custom zenith angles (twilight)
+
+```js
+import { getSpa } from 'nrel-spa';
+
+const civil = getSpa(date, lat, lon, tz, {}, [96]);      // civil twilight
+const nautical = getSpa(date, lat, lon, tz, {}, [102]);  // nautical twilight
+const astro = getSpa(date, lat, lon, tz, {}, [108]);     // astronomical twilight
+
+console.log(civil.customAngles[0].sunrise);   // civil dawn
+console.log(nautical.customAngles[0].sunrise); // nautical dawn
+```
+
+## Options
+
+```js
+const result = getSpa(date, lat, lon, tz, {
+  elevation: 100,    // metres above sea level
+  pressure: 1013.25, // millibars
+  temperature: 15,   // Celsius
+  delta_t: 67,       // ΔT in seconds
+});
+```
+
+## Next steps
+
+- [API Reference](../API-Reference) — full function signatures and return types
+- [Architecture](../Architecture) — module structure and algorithm notes
+- [Advanced Guide](advanced) — twilight, batch calculations, polar scenarios