[feat](trx-frontend): bookmark markers, category colors, text filter

- Move bookmark frequency markers from drawSpectrum() to drawSignalOverlay()
  so dashed lines span both the waterfall and waveform canvases
- Assign distinct palette colors to named categories; uncategorised uses
  --accent-yellow resolved from the live theme at runtime
- Compute WCAG-compliant foreground color (dark/light) per category so label
  text is always legible against the solid background
- Add text search input to the Bookmarks toolbar; filters by name, category,
  and comment client-side without re-fetching from the server

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -1539,9 +1539,9 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   cursor: pointer;
   font-weight: 600;
   font-size: 0.66rem;
-  background: var(--bm-cat-bg, var(--card-bg));
-  color: var(--bm-cat-color, var(--accent-yellow));
-  border: 1px solid var(--bm-cat-border, color-mix(in srgb, var(--accent-yellow) 55%, transparent));
+  background: var(--bm-cat-bg, var(--accent-yellow));
+  color: var(--bm-cat-fg, #1a202c);
+  border: 1px solid var(--bm-cat-bg, var(--accent-yellow));
   border-radius: 3px;
   padding: 2px 8px;
   max-width: 130px;
@@ -1553,11 +1553,10 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   gap: 4px;
 }
 #spectrum-bookmark-axis span:hover {
-  background: var(--bm-cat-bg, color-mix(in srgb, var(--accent-yellow) 28%, transparent));
   filter: brightness(1.15);
 }
 .bm-icon-svg path {
-  fill: var(--bm-cat-color, var(--accent-yellow));
+  fill: var(--bm-cat-fg, #1a202c);
 }
 #spectrum-tooltip {
   display: none;