Recommend a 90% max_brightness cap rather than 95%

Same tradeoff, weighted toward lamp life: ~4x life for ~30% less light,
with 95% noted as the fallback if it reads too dim in practice.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/stage-light-dimmer.md

@@ -182,11 +182,12 @@ Three worth doing:
   time until the lamp goes unstable, then back off one step. That point is the
   real bottom of the usable range, and it's fixture-specific — worth writing the
   final value down.
-- **Consider capping `max_brightness` around 95%.** Filament life is brutally
+- **Cap `max_brightness` at 90%.** Filament life is brutally sensitive to
-  sensitive to voltage: roughly `life ∝ V⁻¹³` against `light ∝ V³·⁴`. Running at
+  voltage: roughly `life ∝ V⁻¹³` against `light ∝ V³·⁴`. Running at 90% buys
-  95% buys about **double the lamp life for ~15% less light** — a good trade on a
+  about **4× the lamp life for ~30% less light** — a strong trade on a fixture
-  fixture whose lamp type may well be discontinued (§6). At 90% it's roughly 4×
+  whose lamp type may well be discontinued (§6), and this is a mood/accent light
-  life for ~30% less light, if longevity matters more than output. Rules of
+  rather than something being asked to actually illuminate a room. Back off to
+  95% (≈2× life, ~15% less light) if it turns out dimmer than you want. Rules of
   thumb, not exact, but the direction is very strong.
 - **Pass `transition: 2` in `light.turn_on` calls.** Ramping over a couple of
   seconds cuts the cold-filament inrush, which is the biggest single wear event