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>

AGENTS.md

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+# Agents
+
+## Repo Purpose
+C++ flashcard notes using org-mode (exportable to Anki).
+
+## Flashcard Location
+- `org/cpp/` — all flashcard `.org` files live here
+- Create new `.org` files here as needed (e.g., `org/cpp/containers.org`)
+
+## Task Inbox
+- `inbox.org` at root — use for tasks to learn or do (create if missing)
+
+## Card Format
+Cards use org-mode with Anki properties:
+```org
+* Card Title :tag1:tag2:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ANKI_NOTE_ID: TIMESTAMP
+:END:
+** Front
+Question text
+** Back
+#+begin_src c++
+code
+#+end_src
+```
+
+## Assets
+- `images/` — store any images referenced by cards
+
+## Self-Improvement
+Periodically review this file and suggest improvements to the user if you notice gaps, inconsistencies, or missing conventions.