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>

package-lock.json

@@ -10,7 +10,6 @@
       "dependencies": {
         "@supabase/supabase-js": "^2.99.3",
         "heic-to": "^1.4.2",
-        "heic2any": "^0.0.4",
         "jspdf": "^4.2.1",
         "jspdf-autotable": "^5.0.7",
         "jszip": "^3.10.1",
@@ -2026,12 +2025,6 @@
       "integrity": "sha512-y69thwxfNcEm2Vk8lbOD/cMabnvMJyOREfJYiCHcXCDqlfcPyJoBhyRc8+iDe1B95LRfpbTOpzxzY1xbRkdwBA==",
       "license": "LGPL-3.0"
     },
-    "node_modules/heic2any": {
-      "version": "0.0.4",
-      "resolved": "https://registry.npmjs.org/heic2any/-/heic2any-0.0.4.tgz",
-      "integrity": "sha512-3lLnZiDELfabVH87htnRolZ2iehX9zwpRyGNz22GKXIu0fznlblf0/ftppXKNqS26dqFSeqfIBhAmAj/uSp0cA==",
-      "license": "MIT"
-    },
     "node_modules/hermes-estree": {
       "version": "0.25.1",
       "resolved": "https://registry.npmjs.org/hermes-estree/-/hermes-estree-0.25.1.tgz",