refactor: table-driven keymap dispatch + auto-derived help list

Replace the global key handling scattered through the main loop with a single
KEYMAP table (key, gate, action, help text) and a DispatchKeymap() pass. The
About/Help overlay now renders its key list straight from the table, so the
on-screen shortcuts can never drift from the actual bindings.

- Order-sensitive keys (Space, Esc) stay inline where their frame ordering
  matters; they carry action==NULL and appear in the table for the help list.
- Adds the F11 fullscreen binding the sidebar button already advertised but
  that was never actually wired up.
- Fix About title em-dash rendering as '?' (font is ASCII-only); use a hyphen.

Launch render verified pixel-identical (AE=0); keys verified via injected input.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ui.c

@@ -578,7 +578,7 @@ void DrawAboutDialog(void)
     DrawRectangle(0, 0, sw, sh, Fade(BLACK, 0.7f));
 
     float pw = 560 * scale;
-    float ph = 470 * scale;
+    float ph = 540 * scale;
     Rectangle panel = { (sw - pw) / 2, (sh - ph) / 2, pw, ph };
     DrawRectangleRec(panel, (Color){ 30, 30, 38, 255 });
     DrawRectangleLinesEx(panel, 2, (Color){ 90, 90, 110, 255 });
@@ -586,7 +586,7 @@ void DrawAboutDialog(void)
     float px = panel.x + 24 * scale;
     float py = panel.y + 20 * scale;
 
-    DrawTextScaled("rspektrum — synchrosqueezed spectrogram viewer", px, py, 18, WHITE);
+    DrawTextScaled("rspektrum - synchrosqueezed spectrogram viewer", px, py, 18, WHITE);
     py += 34 * scale;
 
     // Body lines. NULL = blank spacer; headings start with no leading spaces.
@@ -606,10 +606,6 @@ void DrawAboutDialog(void)
         "    spectral magnitudes.",
         "  - Pixels show synchrosqueezed (reassigned) energy, not raw FFT bins.",
         "  Good to ~a dB for visualization; not lab-grade metrology.",
-        "",
-        "Keys",
-        "  O  open file      P  toggle scope      Home/End  reset / fit view",
-        "  F1 / Esc  close this dialog",
     };
     int n = sizeof(lines) / sizeof(lines[0]);
     for (int i = 0; i < n; i++) {
@@ -619,6 +615,20 @@ void DrawAboutDialog(void)
         py += (s[0] == '\0' ? 8 : 18) * scale;
     }
 
+    // Keys — rendered straight from the keymap table so this list can never
+    // drift from the actual bindings.
+    py += 10 * scale;
+    DrawTextScaled("Keys", px, py, 14, (Color){ 150, 200, 255, 255 });
+    py += 20 * scale;
+    int kn;
+    const KeyBinding* km = GetKeymap(&kn);
+    for (int i = 0; i < kn; i++) {
+        DrawTextScaled(TextFormat("  %-5s %s", km[i].label, km[i].help), px, py, 13, LIGHTGRAY);
+        py += 16 * scale;
+    }
+    DrawTextScaled("  Mouse  wheel = zoom, Alt+drag = pan, drag = select box",
+                   px, py, 13, LIGHTGRAY);
+
     DrawTextScaled("F1 / Esc / click to close", panel.x + pw - 196 * scale,
                    panel.y + ph - 26 * scale, 12, GRAY);
     // Note: opening/closing is handled in the main input loop (not here) so the