Add project docs and initial configuration

- PRD.md: full product requirements for the budget app
- CLAUDE.md: repo guidance including td task management workflow
- AGENTS.md: session startup instructions
- .gitignore: comprehensive ignore rules for Node/React/Docker/editor artifacts

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

CLAUDE.md

@@ -0,0 +1,20 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Task Management
+
+This project uses `td` (a local CLI) for task tracking. At the start of each session:
+
+```bash
+td usage --new-session   # required at conversation start or after /clear
+td usage -q              # quick check for subsequent reads
+```
+
+Optional session labeling:
+```bash
+td session "name"        # label the current session
+td session --new         # force a new session in the same terminal context
+```
+
+Task state is stored in `.todos/issues.db` (SQLite).