refactor: move DSA notes to org/study_deck_02/

Restructure NeetCode study materials into a dedicated Anki-exportable
deck directory. Separates DSA problem notes from C++ flashcards.

- Move roadmap.org from leetcode/out/ to org/study_deck_02/
- Move 200 note files from org/cpp/dsa/ to org/study_deck_02/dsa/
- Add #+PROPERTY: STUDY_DECK_02 to all org files for org-anki export
- Simplify roadmap format: properties drawer replaces nested headings
- Update NEETCODE backlinks in all note files
- Update extract.mjs and scaffold-notes.mjs for new paths
- Create org/study_deck_02/AGENTS.md with study workflow docs
- Update root and leetcode AGENTS.md

org/study_deck_02/dsa/linked-list/0002-add-two-numbers.org

@@ -0,0 +1,18 @@
+* TODO 0002. Add Two Numbers :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0002. Add Two Numbers][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0019-remove-nth-node-from-end-of-list.org

@@ -0,0 +1,18 @@
+* TODO 0019. Remove Nth Node From End of List :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0019. Remove Nth Node From End of List][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0021-merge-two-sorted-lists.org

@@ -0,0 +1,18 @@
+* TODO 0021. Merge Two Sorted Lists :easy:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0021. Merge Two Sorted Lists][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0023-merge-k-sorted-lists.org

@@ -0,0 +1,18 @@
+* TODO 0023. Merge K Sorted Lists :hard:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0023. Merge K Sorted Lists][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0025-reverse-nodes-in-k-group.org

@@ -0,0 +1,18 @@
+* TODO 0025. Reverse Nodes In K Group :hard:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0025. Reverse Nodes In K Group][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0138-copy-list-with-random-pointer.org

@@ -0,0 +1,18 @@
+* TODO 0138. Copy List With Random Pointer :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0138. Copy List With Random Pointer][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0141-linked-list-cycle.org

@@ -0,0 +1,18 @@
+* TODO 0141. Linked List Cycle :easy:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0141. Linked List Cycle][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0143-reorder-list.org

@@ -0,0 +1,18 @@
+* TODO 0143. Reorder List :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0143. Reorder List][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0146-lru-cache.org

@@ -0,0 +1,18 @@
+* TODO 0146. LRU Cache :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0146. LRU Cache][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0206-reverse-linked-list.org

@@ -0,0 +1,18 @@
+* TODO 0206. Reverse Linked List :easy:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0206. Reverse Linked List][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0287-find-the-duplicate-number.org

@@ -0,0 +1,18 @@
+* TODO 0287. Find The Duplicate Number :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0287. Find The Duplicate Number][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/0725-split-linked-list-in-parts.org

@@ -0,0 +1,18 @@
+* TODO 0725. Split Linked List in Parts :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0725. Split Linked List in Parts][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/1472-design-browser-history.org

@@ -0,0 +1,18 @@
+* TODO 1472. Design Browser History :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*1472. Design Browser History][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/1721-swapping-nodes-in-a-linked-list.org

@@ -0,0 +1,18 @@
+* TODO 1721. Swapping Nodes in a Linked List :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*1721. Swapping Nodes in a Linked List][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src

org/study_deck_02/dsa/linked-list/2487-remove-nodes-from-linked-list.org

@@ -0,0 +1,18 @@
+* TODO 2487. Remove Nodes From Linked List :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*2487. Remove Nodes From Linked List][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src