feat: add NeetCode roadmap extractor with dependency graph

- extract.mjs: idempotent script that fetches neetcode.io JS chunks,
  extracts topic dependency graph (18 topics, 21 edges) and problems
  (965 total, 199 NeetCode 150)
- out/roadmap.json: full data (graph + all problems + courses)
- out/roadmap-neetcode150.json: filtered to NeetCode 150 only
- out/roadmap.dot: Graphviz visualization
- out/roadmap.org: org-mode with TODO checklists, Python/C++ links
- neetcode-roadmap-graph.json: standalone edge list
- neetcode-roadmap.dot: standalone DOT file

Also reformats subarray table in qn_00.org

leetcode/neetcode-roadmap.dot

@@ -0,0 +1,55 @@
+// NeetCode Roadmap — Topic Dependency Graph
+// Source: https://neetcode.io/roadmap (chunk 7669)
+// Extracted: 2026-06-01
+//
+// Render: dot -Tpng neetcode-roadmap.dot -o neetcode-roadmap.png
+//   or:   dot -Tsvg neetcode-roadmap.dot -o neetcode-roadmap.svg
+
+digraph NeetCodeRoadmap {
+    rankdir=TB;
+    node [shape=box, style="rounded,filled", fillcolor="#3f4bd1", fontcolor=white, fontname="Helvetica"];
+    edge [color="#555555", arrowsize=0.8];
+
+    // Nodes
+    "1" [label="Arrays &\nHashing"];
+    "2" [label="Two Pointers"];
+    "3" [label="Stack"];
+    "4" [label="Sliding Window"];
+    "5" [label="Linked List"];
+    "6" [label="Binary Search"];
+    "7" [label="Trees"];
+    "8" [label="Tries"];
+    "9" [label="Heap /\nPriority Queue"];
+    "10" [label="Backtracking"];
+    "11" [label="Graphs"];
+    "12" [label="1-D Dynamic\nProgramming"];
+    "13" [label="Intervals"];
+    "14" [label="2-D Dynamic\nProgramming"];
+    "15" [label="Bit Manipulation"];
+    "16" [label="Greedy"];
+    "17" [label="Advanced Graphs"];
+    "18" [label="Math &\nGeometry"];
+
+    // Edges (parentId → node means "parentId is a prerequisite of node")
+    "1" -> "2";
+    "1" -> "3";
+    "2" -> "4";
+    "2" -> "5";
+    "2" -> "6";
+    "5" -> "7";
+    "6" -> "7";
+    "7" -> "8";
+    "7" -> "9";
+    "7" -> "10";
+    "10" -> "11";
+    "10" -> "12";
+    "9" -> "13";
+    "9" -> "16";
+    "9" -> "17";
+    "11" -> "14";
+    "11" -> "17";
+    "11" -> "18";
+    "12" -> "14";
+    "12" -> "15";
+    "15" -> "18";
+}