feat(theme): restore the original palette as the Classic theme

Replace the placeholder Graphite preset with the exact pre-theme-picker
palette (warm paper / ink), reconstructed from styles.css + surfacePage
tokens at commit 746b7e0^. shiki github-light/github-dark, matching the
original markdown/diff highlighting.

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

Author: tridha643

.changeset/classic-theme.md

@@ -0,0 +1,6 @@
+---
+"sideshow": minor
+---
+
+Add a Classic theme to the board theme picker — the original sideshow palette
+(warm paper / ink), restored exactly from the pre-theme-picker styles.

.changeset/graphite-theme.md

@@ -370,38 +370,40 @@ export const THEMES: Theme[] = [
     },
   },
   {
-    id: "graphite",
-    label: "Graphite",
-    shiki: { light: "github-light", dark: "github-dark-dimmed" },
+    // The original sideshow palette (warm paper / ink), restored from the
+    // pre-theme-picker styles.css + surfacePage tokens (commit 746b7e0^).
+    id: "classic",
+    label: "Classic",
+    shiki: { light: "github-light", dark: "github-dark" },
     light: {
-      bg: "#f4f4f5",
-      panel: "#e8e8ea",
+      bg: "#faf9f5",
+      panel: "#f3f2ec",
       surface: "#ffffff",
-      text: "#1d1f24",
-      muted: "#5b5f66",
-      faint: "#8b8f97",
-      border: "#d8dadd",
-      border2: "#bfc2c7",
-      hover: "#e8e8ea",
-      info: { bg: "#e6ebf2", text: "#3f6896", border: "#85a3c9" },
-      success: { bg: "#e6efe8", text: "#3f7d52", border: "#86b395" },
-      warning: { bg: "#f3ecdc", text: "#8a6d33", border: "#cbb077" },
-      danger: { bg: "#f4e3e2", text: "#a6443f", border: "#cf8f8d" },
+      text: "#1a1915",
+      muted: "#5f5e56",
+      faint: "#8e8d83",
+      border: "rgba(20, 20, 10, 0.12)",
+      border2: "rgba(20, 20, 10, 0.25)",
+      hover: "rgba(20, 20, 10, 0.05)",
+      info: { bg: "#e6f1fb", text: "#185fa5", border: "#378add" },
+      success: { bg: "#eaf3de", text: "#3b6d11", border: "#97c459" },
+      warning: { bg: "#faeeda", text: "#854f0b", border: "#ef9f27" },
+      danger: { bg: "#fcebeb", text: "#a32d2d", border: "#e24b4a" },
     },
     dark: {
-      bg: "#1b1c1e",
-      panel: "#232427",
-      surface: "#2a2c30",
-      text: "#e3e4e8",
-      muted: "#a0a3ab",
-      faint: "#71747c",
-      border: "#36383d",
-      border2: "#45474d",
-      hover: "#2f3135",
-      info: { bg: "rgba(127, 166, 214, 0.16)", text: "#7fa6d6", border: "#7fa6d6" },
-      success: { bg: "rgba(126, 186, 148, 0.16)", text: "#7eba94", border: "#7eba94" },
-      warning: { bg: "rgba(212, 178, 110, 0.16)", text: "#d4b26e", border: "#d4b26e" },
-      danger: { bg: "rgba(214, 132, 130, 0.16)", text: "#d68482", border: "#d68482" },
+      bg: "#1f1e1b",
+      panel: "#1a1917",
+      surface: "#2a2925",
+      text: "#eceadf",
+      muted: "#b3b1a4",
+      faint: "#8a887c",
+      border: "rgba(255, 255, 250, 0.12)",
+      border2: "rgba(255, 255, 250, 0.25)",
+      hover: "rgba(255, 255, 250, 0.06)",
+      info: { bg: "rgba(55, 138, 221, 0.18)", text: "#85b7eb", border: "#378add" },
+      success: { bg: "rgba(151, 196, 89, 0.18)", text: "#c0dd97", border: "#97c459" },
+      warning: { bg: "rgba(239, 159, 39, 0.18)", text: "#fac775", border: "#ef9f27" },
+      danger: { bg: "rgba(226, 75, 74, 0.18)", text: "#f09595", border: "#e24b4a" },
     },
   },
 ];