Retire the Dashboard tab; Processes is the front page

The app repeated itself. The module list, /api/prefs/dashboard, applyPrefs and the
per-user dashboard blob are gone. Widgets stays and now says plainly that it is for
dashboards outside Ham Lab.

This also closes a bug: applyPrefs set the sampling rate from intervalMs inside the
dashboard layout, and reset it to the default when that field was absent — so with
per-user layouts, one account saving a dashboard could reset the sampling rate for the
whole machine. The sampler now has one source.

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

web/src/Files.tsx

@@ -1,6 +1,6 @@
 import { DragEvent, useCallback, useEffect, useRef, useState } from 'react'
 import { api, FileEntry, FileInfo } from './api'
-import { fmtBytes } from './Dashboard'
+import { fmtBytes } from './fmt'
 import { Btn, Loading, Spinner, askText, askYes, setUnsaved, toast, useEscape } from './ui'
 import { useHashSel } from './hashsel'