feat: LED strips — editor notes, docs, demo, smokes, golden scenes, profile (#780)

Stage 5 of #780.

- Import summary: «Strips left unbound after import: {n}» from the backend
  `unbound_led_strips` count; «Optimize plans» reports strips passing
  through walls per space and edits none (AC16).
- Linear field for long strips (ТЗ §13.2): pieces of at most the radius
  along the polyline, emitters thinned to r/4, each piece clipped to the
  visibility fans of its own emitters as separate clipPath children (no
  boolean pass per piece), one floor clip for the whole layer, no fan at
  all where nothing blocks within the radius; a grid index of body faces
  and boxed inside tests; unchanged fields skip re-diffing. 50×50 on the
  large house: first stable frame ~1.4 s, warm space ~1.1 s locally.
- led-strips-v1 profile: demo/benchmark_led_strips.mjs with the derived
  large-house fixture (10×5, 50×50, none), absolute limits of the ТЗ table
  in demo/performance/budgets-led-strips.json, exact counters (zero
  recomputes on HA ticks/camera/colour, ≤50 cache entries, no growth over
  20 cycles); added to the full performance workflow.
- Bundle: LAZY_LED_GZIP_CEILING 10 KiB, LAZY_LED_EDITOR_GZIP_CEILING 11 KiB
  (measured + 10 %, rounded up); overlaps with the initial and editor
  graphs refused; the lazy editor graph stays inside its ceiling.
- Smokes smoke_led_strip_draw/bind/glow, linked in smoke-links; 13 mutants
  in the registry (7 browser guards in the inventory); config field registry
  entry `spaces[].led_strips`.
- Golden: five new scenes on the `golden-led` space of the visual fixture
  (`ledStrips` option, the designer's four strips on #868D94), matrix v71.
- Docs: LIGHT, DEVICE-PRESENTATION, USER-GUIDE (en/ru), UX-MODES,
  ARCHITECTURE, ISOMETRIC, CONFIG-COMPATIBILITY, TOUCH-SUPPORT, demo/stand
  README, performance README; docs/design/led-strips with the unchanged
  designer archive, two paired frames and ACCEPTANCE.md; both changelogs.

Issue: #780
User-Visible: yes

docs/UX-MODES.md

@@ -249,6 +249,22 @@ layer you cannot see is a layer you cannot edit.
   👁 "Show hidden" (local editor tool; replaced the shared show-all toggle),
   ⬡ icon rules.
 
+- **LED strip** (#780) — the only place a strip is drawn or edited. The tool
+  sits next to «Add»; it is a temporary drawing mode inside Devices, not a
+  separate editor. Clean clicks add points (pan, pinch, a second finger,
+  cancel and the synthetic click after navigation never do), snapping to the
+  grid and to physical wall faces / zero-wall axes; a new segment stops at
+  the first face of masonry, a partition, a column or a window. `Ctrl/Cmd+Z`
+  removes the chain's own point first, `Esc` finishes. A finished strip opens
+  the device picker. A clicked strip is selected (session state only) and
+  shows vertex handles and the LED branch of the secondary tray. An ordinary
+  icon clicked while a strip is selected still opens its own dialog. The
+  device dialog switches the representation («Show as LED strip» / «Show as
+  icon»). Geometry and representation changes are LED commands of the same
+  device history; the stack still never absorbs marker settings or
+  Plan/Background edits. Plan and Background show strips as a passive
+  translucent mark only — no tool, handles or targets.
+
 ## Background — the decor underlay
 
 - Toolbar tools: Select / optional Plan backdrop / Line / Rectangle / Oval /