feat: add iterator flashcards, sync script, and project scaffolding

- iterator.org: C++ iterator flashcard deck
- questions.org: LeetCode question index (217, 242)
- inbox.org: learning inbox with two-sum implementation and notes
- sync-anki.sh: batch sync org files to Anki via emacsclient
- AGENTS.md: conventions for AI agents working in this repo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

org/cpp/iterator.org

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+* What is a C++ iterator :cpp:iterator:concept:recognition:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491263
+:END:
+** Front
+What is an iterator in C++?
+** Back
+An object that points to elements in a container and allows traversal through them, providing a common interface for accessing elements sequentially without exposing the underlying structure.
+
+* Task: Traverse a vector with iterators :cpp:iterator:production:code:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491259
+:END:
+** Front
+Write C++ code to iterate through a std::vector<int> using iterators
+** Back
+#+begin_src c++
+std::vector<int> vec = {1, 2, 3};
+for (auto it = vec.begin(); it != vec.end(); ++it) {
+    std::cout << *it << " ";
+}
+#+end_src
+
+* Iterator operations :cpp:iterator:concept:enumeration:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491255
+:END:
+** Front
+What are the four required operations for a C++ iterator?
+** Back
+- `operator*` — dereference to get current element
+- `operator++` — advance to next element (pre and post)
+- `operator==` — equality comparison
+- `operator!=` — inequality comparison
+
+* cpp iterator categories :cpp:iterator:concept:enumeration:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491250
+:END:
+** Front
+List the five iterator categories in C++ (from simplest to most advanced)
+** Back
+1. Input Iterator — read values, advance once
+2. Output Iterator — write values, advance once
+3. Forward Iterator — read/write, multiple passes
+4. Bidirectional Iterator — + operator--
+5. Random Access Iterator — + arithmetic, subscript
+
+* Task: Use const iterator :cpp:iterator:production:code:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491246
+:END:
+** Front
+Write C++ code to safely traverse a const std::vector without modifying elements
+** Back
+#+begin_src c++
+std::vector<int> vec = {1, 2, 3};
+for (auto it = vec.cbegin(); it != vec.cend(); ++it) {
+    std::cout << *it << " ";
+}
+#+end_src
+
+* Task: Use reverse iterator :cpp:iterator:production:code:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491241
+:END:
+** Front
+Write C++ code to iterate backwards through a std::vector
+** Back
+#+begin_src c++
+std::vector<int> vec = {1, 2, 3};
+for (auto it = vec.rbegin(); it != vec.rend(); ++it) {
+    std::cout << *it << " ";
+}
+#+end_src
+
+* Minimal custom iterator implementation :cpp:iterator:implementation:production:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491237
+:END:
+** Front
+Write the minimal C++ code to implement a forward iterator for a custom class
+** Back
+#+begin_src c++
+class MyIterator {
+    Node* ptr;
+public:
+    reference operator*() const { return ptr->data; }
+    pointer operator->() const { return &ptr->data; }
+    MyIterator& operator++() { ptr = ptr->next; return *this; }
+    MyIterator operator++(int) { auto tmp = *this; ++*this; return tmp; }
+    bool operator==(const MyIterator& other) const { return ptr == other.ptr; }
+    bool operator!=(const MyIterator& other) const { return !(*this == other); }
+};
+#+end_src
+
+* When to use iterators vs indices :cpp:iterator:concept:comparison:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: 1776621491226
+:END:
+** Front
+When would you choose iterators over index-based loops in C++?
+** Back
+- Container type is unknown or could change (iterators abstract the container)
+- Using standard library algorithms (std::find, std::sort, etc.)
+- Need to traverse multiple containers simultaneously
+- Working with containers without random access (list, map)
+- Decouple algorithm from container structure