Split settings into tabs; exposure and focus on the home screen

Home screen gains shutter, aperture and ISO as dropdowns plus a focus stepper
(three nudge sizes each way, and AF) where the body drives focus over PTP.
Those three drop out of the read-only strip rather than being shown twice.

Everything is built from what the camera actually reports, so a body without
one of these controls doesn't get it rather than showing something that
silently fails. The 450D marks shutter and aperture readonly unless the mode
dial is somewhere they apply, so the dropdowns disable themselves and say why.
Focus uses the EOS manualfocusdrive steps and autofocusdrive, and warns when
live view is off, which Canon bodies generally require for focus commands.

The settings drawer is now tabbed: app settings stay on the first tab, and
each config section the camera reports gets its own. Empty sections are
dropped, and a selected section that disappears falls back to the first tab.
Tabs wrap rather than scroll - a scrolled-off tab is an undiscoverable one.

Reverts the automatic camera search added in the previous commit, restoring
the Select camera button. Auto-connect could park with no way to reach the
device chooser: WebUSB permissions are per-origin, so a grant on localhost
doesn't carry to the deployed copy, and a camera that's asleep or held by
another app never arrives.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QK7PKpRVoy69Fpa32R8abb

examples/preact/types.d.ts

@@ -6,12 +6,8 @@ type LogEntry = {
 };
 
 type AppState = {
-  /**
-   * Which top-level screen is showing. 'searching' auto-retries in the
-   * background; 'permission' is the one-off WebUSB grant, which the browser
-   * will not let us trigger without a click.
-   */
-  view: 'status' | 'searching' | 'permission' | 'ready';
+  /** Which top-level screen is showing. */
+  view: 'status' | 'picker' | 'ready';
   /** Shown while `view` is 'status'. */
   message?: string;
   config?: import('web-gphoto2').Config;