Palette calibration: precise hex/RGB inputs instead of a color picker

A native <input type="color"> swatch can't be typed into precisely --
no way to enter an exact measured value. Replaced with a small table:
a read-only preview swatch, a hex text field, and three 0-255 number
fields (R/G/B) per ink color, kept in sync live in both directions
(editing hex updates R/G/B and the swatch; editing any of R/G/B updates
hex and the swatch). Hex stays the field actually read at save time --
the server-side validation (#rrggbb via hex_to_rgb) is unchanged, this
is a client-side-only swap of the input widget.

server/app/static/theme.css

@@ -168,28 +168,33 @@ summary.card-title { cursor: pointer; margin-bottom: 0; }
 details.card[open] summary.card-title { margin-bottom: 14px; }
 details.card .sub { margin-top: 8px; }
 
-.palette-grid {
-  display: grid;
-  grid-template-columns: repeat(auto-fit, minmax(110px, 1fr));
-  gap: 12px;
-  margin-top: 14px;
+.palette-table-wrap { overflow-x: auto; margin-top: 14px; }
+.palette-table { width: 100%; border-collapse: collapse; font-size: 13px; }
+.palette-table th {
+  text-align: left;
+  color: var(--text-muted);
+  font-weight: 600;
+  font-size: 11.5px;
+  text-transform: uppercase;
+  letter-spacing: 0.02em;
+  padding: 0 8px 8px 0;
 }
-.palette-swatch {
-  display: flex;
-  align-items: center;
-  gap: 8px;
-  margin-top: 0;
-  font-size: 13px;
-  font-weight: 500;
-  color: var(--text);
+.palette-table td { padding: 4px 8px 4px 0; vertical-align: middle; }
+.palette-table input { margin-top: 0; }
+.palette-swatch-preview {
+  display: block;
+  width: 22px;
+  height: 22px;
+  border-radius: 6px;
+  border: 1px solid var(--border);
 }
-.palette-swatch input[type="color"] {
-  width: 34px;
-  height: 34px;
-  padding: 2px;
-  margin-top: 0;
-  border-radius: 8px;
-  cursor: pointer;
+.palette-table input.palette-hex {
+  width: 92px;
+  font-family: ui-monospace, "SF Mono", Consolas, monospace;
+  text-transform: lowercase;
+}
+.palette-table input.palette-rgb {
+  width: 58px;
 }
 
 .card {