polish(v0.6): replace toolbar emoji with themed line icons + hover tooltips

The glossy emoji (🔍⚙▦🕘⌨🔗📱) clashed with the Amber dark theme. Swap them
for clean lucide line icons (MIT, stroke=currentColor) so they take the theme
colour — muted by default, Amber on hover — and add a styled CSS hover tooltip
(data-tip, right-anchored so it never clips the edge) showing what each does.

- public/icons.ts: 7 line icons (search/settings/dashboard/history/keyboard/
  share/device), script-generated from lucide
- 7 toolbar modules: innerHTML = ICON_* + data-tip + aria-label
- style.css .toolbtn: 18px svg, --text-dim → --accent on hover, [data-tip] tooltip

Frontend-only. web typecheck + build clean; bundle has 0 toolbar emoji; verified
in-browser: line icons in theme colour, amber + tooltip on hover.

public/style.css

@@ -237,20 +237,50 @@ body {
   border-left: 1px solid var(--border);
 }
 .toolbtn {
+  position: relative; /* for the hover tooltip */
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
   background: none;
   border: none;
   color: var(--text-dim);
   cursor: pointer;
-  font-size: 15px;
   padding: 7px 9px;
   border-radius: 8px;
   line-height: 1;
-  transition: background 0.12s ease;
+  transition: background 0.12s ease, color 0.12s ease;
+}
+.toolbtn svg {
+  display: block;
+  width: 18px;
+  height: 18px;
 }
 .toolbtn:hover {
-  color: #fff;
+  color: var(--accent);
   background: var(--surface-2);
 }
+/* Hover tooltip (right-anchored so it never clips the screen edge). */
+.toolbtn[data-tip]::after {
+  content: attr(data-tip);
+  position: absolute;
+  top: calc(100% + 6px);
+  right: 0;
+  white-space: nowrap;
+  background: var(--surface-3);
+  color: var(--text);
+  border: 1px solid var(--border-strong);
+  padding: 4px 8px;
+  border-radius: 6px;
+  font-size: 12px;
+  font-weight: 500;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 0.12s ease;
+  z-index: 60;
+}
+.toolbtn[data-tip]:hover::after {
+  opacity: 1;
+}
 
 /* ── Terminal area ───────────────────────────────────────────────── */
 #term {