cleanup: remove dead code, drop unused deps, refactor derived-state effects

Lint went from 84 problems to 0. Build passes.

Dead code:
- TeamInvoices: drop the orphaned Subcontractor PO block (updateSubcontractorPO
  plus send/ready-to-pay/paid/reopen/cancel/delete/download/CPA-export handlers
  and ~25 derived vars). That feature moved to the routed
  TeamCreateSubcontractorPO / TeamSubcontractorPODetail pages in the Layout2
  redesign; these were leftovers. 2100 -> 1880 lines.
- Tasks: drop unrendered project sort/tab/completion logic in TasksPageShell.
- Remove 59 unused vars, imports, and handlers across 12 other files.

Removed wasted queries:
- TeamInvoices ran a nested subcontractor_payments join (profiles, projects,
  companies, PO items, tasks) on every page load into state nothing read.
- TeamInvoices and ExternalMyInvoices each fetched a task-type map on invoice
  open and discarded it; the ExternalMyInvoices one blocked the detail popup.
- RequestForm queried sign_families on mount into unread state.

Dependencies:
- Drop heic2any (zero imports). heic-to is the one in use and already lazy-loads.

Effects and exports:
- RequestForm: remove 4 effects. Sign-row sizing and company-change resets move
  into their change handlers; single-company selection is derived during render
  rather than written back into form state.
- FilterDropdown: measure position on click instead of in an effect, which also
  removes a one-frame stale-position flicker.
- BrandBook: latest-ref pattern so the 900ms address debounce is not reset by
  handler identity.
- ClientMyInvoices: hoist MONTHS to module scope.
- Split non-component exports: POPUP_FIELD_LABEL moves to lib/popupStyles.js;
  resolveProfileAvatar and useLiveClock are internal-only; getGreeting deleted
  as nothing referenced it.

Companies.jsx keeps one scoped eslint-disable with a reason: load() only
setStates after awaiting its queries, so set-state-in-effect is a false positive
there, and load() is shared with the create/delete handlers.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/InvoiceDetailPopup.jsx

@@ -1,16 +1,6 @@
 import { popupOverlayStyle, popupSurfaceStyle } from '../lib/popupStyles';
 import PageLoader from './PageLoader';
 
-export const POPUP_FIELD_LABEL = {
-  fontSize: 11,
-  fontWeight: 500,
-  color: 'var(--text-secondary)',
-  textTransform: 'uppercase',
-  letterSpacing: 0.8,
-  display: 'block',
-  marginBottom: 4,
-};
-
 export default function InvoiceDetailPopup({
   title,
   subtitle,