fix(settings/providers): drop colour palette + filter polish + drawer warnings

Round of design-feedback fixes.

Provider chips
- Drop the per-provider raw Tailwind palette (bg-blue-600 etc.) from
  Provider::Metadata. All cards + drawer logo lock-up now use
  bg-surface-inset + text-primary, matching the design's §04 "drop
  colour entirely" recommendation. Solves the long-standing §01
  BLOCKER without externalising brand assets. Re-introducing logos
  later just means an optional logo_svg: field on metadata.
- ProviderCard component drops the `logo_bg:` parameter; the chip
  is now styled in the template.

Filter / search
- "Available · N" count and the empty-filter state now update
  client-side as the chip filter and free-text search narrow the
  grid (new `count` Stimulus target + dedicated update path).
- Empty-filter state now offers a Clear filters button that resets
  both the search input and the active chip in one click.
- Search placeholder drops the drifting "Search 9 providers" count
  for plain "Search providers" — the section heading carries the
  number.
- Chip labels normalised to plural where natural: "Banks · Crypto ·
  Investments" (Crypto stays as the mass noun).

Drawer copy / treatment
- "IP Whitelisting Required" → "IP whitelisting required" (DS
  sentence-case).
- Binance "do NOT enable withdrawal permissions" lifted out of
  inline red-text into a proper bg-warning-50 border-warning-200
  alert block with an alert-triangle icon. Matches the api_keys /
  hosting alert pattern.
- SnapTrade free-tier inline alert-triangle now uses `size: "sm"`
  so the icon stops rendering at 20px next to 14px body text.

Spacing
- Group-heading margin top bumped 5 → 6 (20→24px) so the eyebrow
  has more breathing room above the search bar.

app/javascript/controllers/providers_filter_controller.js

@@ -2,8 +2,10 @@ import { Controller } from "@hotwired/stimulus";
 
 // Connects to data-controller="providers-filter"
 // Filters provider cards by free-text query and a chip-selected kind.
+// Updates the visible-count target on the section heading and toggles
+// an empty-state target when no card matches.
 export default class extends Controller {
-  static targets = ["input", "chip", "card", "empty"];
+  static targets = ["input", "chip", "card", "empty", "count"];
   static values = { kind: { type: String, default: "all" } };
 
   connect() {
@@ -29,6 +31,10 @@ export default class extends Controller {
       if (visible) visibleCount++;
     });
 
+    if (this.hasCountTarget) {
+      this.countTarget.textContent = visibleCount;
+    }
+
     if (this.hasEmptyTarget) {
       this.emptyTarget.classList.toggle("hidden", visibleCount > 0);
     }
@@ -40,6 +46,14 @@ export default class extends Controller {
     this.filter();
   }
 
+  clear() {
+    if (this.hasInputTarget) this.inputTarget.value = "";
+    this.kindValue = "all";
+    this.syncChipState();
+    this.filter();
+    if (this.hasInputTarget) this.inputTarget.focus();
+  }
+
   syncChipState() {
     if (!this.hasChipTarget) return;
     this.chipTargets.forEach((chip) => {