Rename split-loop-with-lambda to slice-with-lambda

The refactoring is now published as Slice on sammancoaching.org:
https://sammancoaching.org/refactorings/slice.html

- git mv ideas/split-loop-with-lambda -> ideas/slice-with-lambda
- rename learning-hour file and update frontmatter name
- update paths in tools/rehearse scripts and report title
- update prose: 'Split Loop with Lambda' -> 'Slice with Lambda'
  in learning hour, exercise READMEs, storyboard, solution comments
- link the published Slice refactoring from the pattern draft

ideas/slice-with-lambda/storyboard/svg/04-pure-test.svg

@@ -0,0 +1,51 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+    <marker id="arrGr" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#16a34a"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Step 5-lite — test through the seam with a pure lambda</text>
+  <text x="24" y="56" font-size="13" fill="#16a34a" font-weight="bold">The test passes alwaysSunny. Scorer is never touched: no Random, deterministic, glanceable.</text>
+
+  <!-- test -->
+  <rect x="50" y="160" width="230" height="130" rx="10" fill="#f0fdf4" stroke="#16a34a" stroke-width="1.5"/>
+  <text x="66" y="186" font-size="13" font-weight="bold" fill="#14532d">LongRangeForecastsTest</text>
+  <text x="66" y="210" font-size="10" fill="#475569">LongFunction&lt;Boolean&gt;</text>
+  <text x="66" y="232" font-size="12" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#16a34a">alwaysSunny = days -&gt; true</text>
+  <text x="66" y="258" font-size="11" font-family="Menlo, Consolas, monospace" fill="#14532d">longRangeForecast(alwaysSunny)</text>
+
+  <!-- middle: overload -->
+  <rect x="340" y="150" width="180" height="170" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="354" y="176" font-size="11" font-weight="bold" fill="#0f172a">longRangeForecast(<tspan fill="#9333ea">λ</tspan>)</text>
+  <text x="354" y="204" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">collectExpected-</text>
+  <text x="354" y="220" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">Weather(<tspan fill="#9333ea" font-weight="bold">λ</tspan>)</text>
+  <text x="354" y="248" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">reset loop</text>
+  <text x="354" y="274" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">scoring loop</text>
+  <text x="354" y="296" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">+= 10 / +5 / +2</text>
+
+  <!-- right: extracted method -->
+  <rect x="560" y="150" width="170" height="170" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="574" y="176" font-size="10" font-weight="bold" fill="#0f172a">collectExpectedWeather(λ)</text>
+  <text x="574" y="204" font-size="10" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for d : DATES</text>
+  <text x="574" y="226" font-size="10" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">expected.add(<tspan fill="#9333ea" font-weight="bold">λ</tspan>.apply(d))</text>
+  <text x="574" y="252" font-size="10" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">return expectedWeather</text>
+  <text x="574" y="290" font-size="10" fill="#16a34a" font-weight="bold">pure ✓</text>
+
+  <!-- green arrows -->
+  <line x1="284" y1="225" x2="334" y2="225" stroke="#16a34a" stroke-width="1.5" marker-end="url(#arrGr)"/>
+  <text x="286" y="214" font-size="10" fill="#16a34a">alwaysSunny</text>
+  <line x1="524" y1="225" x2="554" y2="225" stroke="#16a34a" stroke-width="1.5" marker-end="url(#arrGr)"/>
+
+  <!-- scorer, never called -->
+  <rect x="560" y="370" width="170" height="56" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="4 3" opacity="0.8"/>
+  <text x="645" y="392" font-size="12" font-weight="bold" fill="#94a3b8" text-anchor="middle">Scorer</text>
+  <text x="645" y="412" font-size="10" fill="#64748b" text-anchor="middle">never called by the test ✗</text>
+  <line x1="645" y1="368" x2="645" y2="326" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <text x="655" y="350" font-size="11" font-weight="bold" fill="#dc2626">✗</text>
+
+  <text x="50" y="430" font-size="12" fill="#475569">Approved: {Strawberry:12, Chocolate:12, Vanilla:17, } — every run, not just a lucky roll.</text>
+</svg>