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/stack/0020-valid-parentheses.org

@@ -0,0 +1,18 @@
+* TODO 0020. Valid Parentheses :easy:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0020. Valid Parentheses][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/stack/0084-largest-rectangle-in-histogram.org

@@ -0,0 +1,18 @@
+* TODO 0084. Largest Rectangle In Histogram :hard:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0084. Largest Rectangle In Histogram][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/stack/0150-evaluate-reverse-polish-notation.org

@@ -0,0 +1,18 @@
+* TODO 0150. Evaluate Reverse Polish Notation :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0150. Evaluate Reverse Polish Notation][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/stack/0155-min-stack.org

@@ -0,0 +1,18 @@
+* TODO 0155. Min Stack :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0155. Min Stack][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/stack/0682-baseball-game.org

@@ -0,0 +1,18 @@
+* TODO 0682. Baseball Game :easy:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0682. Baseball Game][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/stack/0726-number-of-atoms.org

@@ -0,0 +1,18 @@
+* TODO 0726. Number of Atoms :hard:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0726. Number of Atoms][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/stack/0739-daily-temperatures.org

@@ -0,0 +1,18 @@
+* TODO 0739. Daily Temperatures :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0739. Daily Temperatures][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/stack/0853-car-fleet.org

@@ -0,0 +1,18 @@
+* TODO 0853. Car Fleet :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0853. Car Fleet][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/stack/0901-online-stock-span.org

@@ -0,0 +1,18 @@
+* TODO 0901. Online Stock Span :medium:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*0901. Online Stock Span][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/stack/1544-make-the-string-great.org

@@ -0,0 +1,18 @@
+* TODO 1544. Make The String Great :easy:
+#+PROPERTY: STUDY_DECK_02
+:PROPERTIES:
+:NEETCODE: [[../../roadmap.org::*1544. Make The String Great][Roadmap]]
+:END:
+
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
+#+begin_src cpp
+
+#+end_src