graph: interactive liveliness (drag/pan/zoom, unlinked toggle, label colors)

Backend /api/graph now returns ALL non-trashed notes as nodes, each with its
first label's color; edges unchanged. GraphView reworked: drag a node to
reposition it (pins to cursor + reheats the sim), pan the background, wheel-
zoom toward the cursor, a "Show unlinked notes" toggle (connected-only by
default), a Reset view button, and nodes filled by label color. Click (a
press without a drag) still opens the note; re-fetches on view open.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/notes/colors.ts

@@ -57,6 +57,21 @@ export const LABEL_CHIP_CLASSES: Record<NoteColor, string> = {
   gray: "bg-neutral-200 text-neutral-700 dark:bg-neutral-700 dark:text-neutral-200",
 };
 
+// Solid fills for graph nodes (SVG needs concrete colors, not Tailwind bg classes).
+// Mid-tone hues read on both the light and dark graph background.
+export const NOTE_NODE_FILL: Record<NoteColor, string> = {
+  default: "#9ca3af",
+  red: "#ef4444",
+  orange: "#f97316",
+  yellow: "#f59e0b",
+  green: "#22c55e",
+  teal: "#14b8a6",
+  blue: "#3b82f6",
+  purple: "#a855f7",
+  pink: "#ec4899",
+  gray: "#6b7280",
+};
+
 export const NOTE_COLOR_LABELS: Record<NoteColor, string> = {
   default: "Default",
   red: "Red",