Add a ?pi=1 profile, and stop re-deriving search keys per keystroke

Two separate costs, both measured on musicdolphin (Pi 4, 1920x1080 kiosk), where the
app was burning ~70% of a core with nothing happening on screen.

Per-frame work. The ambient canvas repaints a full-screen gradient plus a particle
field every frame, and `usePlaybackClock` pushes a React setState per animation frame
into both PlayView and PlayerBar for the whole length of a track. `?pi=1` (lib/
lowPower.ts) makes those cheaper rather than switching them off: the canvas paints a
quarter of the pixels at 30fps with a bubble cap, and the clock renders ten times a
second - a progress bar advances one pixel every few hundred ms and its label has
one-second resolution, so nothing on screen can tell. Only the effects with no cheap
version actually go: the backdrop-filter glass blur and the decorative CSS loops.
Also drops a redundant full-canvas clearRect that the opaque gradient always covered.

Search. normalize() runs a Unicode NFD decomposition, and albumMatches/songMatches
called it on every album title and every track title on every keystroke - 4969 of them
for a track search, whose answer cannot change until the library does. buildSearchIndex
does it once per library payload; a keystroke is now String.includes over strings that
already exist. On the real library that is 33ms -> 3.4ms for an eight-letter track
query on a laptop, and this runs on a Pi. The same index partitions albums by shelf and
pre-sorts each shelf's categories, which App and BrowseView were deriving separately
from the same data.

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

web/src/lib/theme.ts

@@ -11,6 +11,7 @@
 
 import type { CSSProperties } from "react";
 
+import { LOW_POWER } from "./lowPower";
 import type { Group } from "./search";
 import type { UiState } from "./keyboard";
 
@@ -36,20 +37,26 @@ export const ANIMATE_VIEW_TRANSITIONS = true;
 
 /** Frost the glass panels/cards/rows with a real backdrop blur. `backdrop-filter` is
  * one of the most GPU-expensive CSS effects in the app - a live backdrop copy+blur
- * per element, repeated for every album card in the unvirtualized grid - so turn
- * this off on weak hardware (e.g. an old Raspberry Pi) to fall back to a plain
- * translucent background with no blur. */
-export const SHOW_GLASS_BLUR = true;
+ * per element, repeated for every album card in the unvirtualized grid - and unlike
+ * the canvas there is no cheaper version of it to fall back to, so `?pi=1` switches
+ * it off outright: a plain translucent background, no blur. This is the one visible
+ * cost of the Pi profile. */
+export const SHOW_GLASS_BLUR = !LOW_POWER;
 
 /** Render the play view's animated canvas background (gradient + bubbles, both
  * redrawn every frame at 60fps). Off falls back to `.stage`'s own static CSS
- * gradient, which is still underneath the canvas either way. */
+ * gradient, which is still underneath the canvas either way.
+ *
+ * Deliberately still on under `?pi=1`: it is the app's whole look, and
+ * `AMBIENCE_QUALITY` in lib/lowPower.ts makes it affordable (quarter of the pixels,
+ * half the frames) rather than making it go away. */
 export const SHOW_AMBIENCE = true;
 
 /** Run the purely decorative CSS animation loops: the room page's bubble field and
- * the dolphin mascot's bob/swim. Individually cheap (opacity/transform only) but
- * free to cut on weak hardware. */
-export const SHOW_DECORATIVE_ANIMATIONS = true;
+ * the dolphin mascot's bob/swim. Individually cheap (opacity/transform only), but
+ * a couple of dozen elements animating forever still means a repaint every frame on
+ * a machine compositing in software, and they carry no information. */
+export const SHOW_DECORATIVE_ANIMATIONS = !LOW_POWER;
 
 // ------------------------------------------------------------------ colors --