feat(calibration): browser-driven auto edge-calibration UI (phase 3)

Reusable, chase-driven calibration flow that solves + saves the linear
CalibrationConfig with a few taps — no LED counting — and works in the
browser on desktop and Android (no Tkinter dependency).

- features/auto-calibration.ts: 5-step flow (start corner -> direction ->
  tap-to-mark-corners -> solved preview -> save). Drives the phase-1 session
  endpoints (session/position/solve) and persists via PUT /color-strip-
  sources/{id}. cornerIndices[0] is anchored to strip index 0 per the solver
  contract. unmountAutoCalibration() is the single cleanup gate — the
  calibration session is always stopped (device restored) on cancel, modal
  close, after save, AND on a mid-flow error, so the strip is never left dark
  or stuck.
- Public API mountAutoCalibration({container, cssId, deviceId, onComplete,
  onCancel}) for the phase-4 wizard to embed; showAutoCalibration() standalone.
- "Auto-calibrate" entry added to the existing calibration modal; standalone
  modal template; app.ts/global.d.ts exports; .autocal-* CSS matching the
  ds-section vocabulary; 43 autocal.* i18n keys in en/ru/zh; docs/CALIBRATION.md.

Part of the edge-calibration + first-run-wizard feature (Big Bang; intermediate
phase — full build/suite + test-writer gated at the final phase).

docs/CALIBRATION.md

@@ -54,7 +54,48 @@ When you attach a device, a default calibration is created:
 }
 ```
 
-## Custom Calibration
+## Automatic Calibration
+
+The easiest way to calibrate your strip is the **Auto-Calibrate** wizard, available directly
+from the calibration modal. No LED counting required — just answer three questions and tap four
+corners.
+
+### Prerequisites
+
+- A **Color Strip Source** (not a device-only target) associated with the strip.
+- A **WLED device** connected and reachable by LedGrab.
+
+### How to Start
+
+1. Open the **Calibration** modal for your strip source (pencil icon → Calibration tab).
+2. Click the **Auto-calibrate** button in the modal footer.
+3. Follow the five-step wizard.
+
+### Wizard Steps
+
+| Step | What you do |
+| ---- | ----------- |
+| 1. Device | Select the WLED device that drives the strip. |
+| 2. Start corner | LED #0 lights up on your device. Tap the corner where you see it. |
+| 3. Direction | Sweep a few LEDs light up in sequence. Tap the direction they move. |
+| 4. Mark corners | Use the step buttons to sweep to each remaining corner, then tap **Mark corner**. Repeat for all 4 corners. |
+| 5. Preview & Save | Review the detected layout (start position, direction, LED counts per edge). Click **Save** to apply. |
+
+### What Happens in the Background
+
+- A calibration session takes exclusive control of the device for the duration of the wizard;
+  any previously running effect is paused and automatically restored when the wizard exits
+  (whether by saving, cancelling, or closing the modal).
+- The solved `CalibrationConfig` is written directly to the Color Strip Source via the existing
+  PUT endpoint and takes effect immediately (no restart needed).
+
+### Tips
+
+- If LED #0 is hard to see, reduce ambient lighting briefly.
+- The wizard works in the browser — desktop and Android TV app both supported.
+- If you make a mistake in step 4, use **Step back** to re-mark the previous corner.
+
+## Manual Calibration
 
 ### Step 1: Identify Your LED Layout