Add API Explorer app

Development app with ingress support for inspecting Supervisor ingress
proxy headers and testing Home Assistant Core API calls. Provides a
web UI with an ingress header inspector, API request builder, and
quick action presets for common endpoints.

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

Author: agners

api_explorer/DOCS.md

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+# API Explorer
+
+## About
+
+API Explorer is a development and debugging tool for Home Assistant app and integration developers. It lets you see exactly what Supervisor's ingress proxy does to requests and test Core API endpoints without leaving the browser.
+
+## Panels
+
+### Ingress Headers
+
+Displays all HTTP headers arriving at the app after Supervisor's ingress proxy has processed the request. Useful for verifying that user identity headers (`X-Remote-User-Id`, `X-Remote-User-Name`, `X-Remote-User-Display-Name`) and forwarding headers (`X-Forwarded-For`, `X-Forwarded-Host`, `X-Forwarded-Proto`) are set correctly.
+
+### API Request Builder
+
+Send arbitrary HTTP requests to the Home Assistant Core API via the Supervisor proxy. The app authenticates using its `SUPERVISOR_TOKEN` automatically. The full response (status code, headers, and body) is displayed for inspection.
+
+### Quick Actions
+
+One-click buttons for commonly used API endpoints: status, config, states, services, and events.
+
+## Configuration
+
+This app has no configuration options. It uses `homeassistant_api: true` to access the Core API through Supervisor.

api_explorer/Dockerfile

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+ARG BUILD_FROM
+FROM ${BUILD_FROM}
+
+RUN pip3 install --no-cache-dir aiohttp==3.11.12
+
+COPY rootfs /

api_explorer/README.md

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+# API Explorer
+
+A development app for Home Assistant that provides a web UI (via ingress) to inspect Supervisor ingress behavior and test Home Assistant Core API calls.
+
+## What it does
+
+- **Ingress Header Inspector**: Shows all HTTP headers that Supervisor's ingress proxy sends to apps, including `X-Remote-User-Id`, `X-Remote-User-Display-Name`, `X-Forwarded-For`, etc.
+- **API Request Builder**: Make API calls to Home Assistant Core through the Supervisor proxy (`http://supervisor/core/api/...`) with configurable method, path, headers, and JSON body.
+- **Quick Actions**: Preset buttons for common Core API endpoints like `/api/states`, `/api/config`, and `/api/services`.
+
+## Usage
+
+1. Copy this folder to `/addons/` on a Home Assistant OS or Supervised system
+2. In the HA UI: Settings > Apps > App Store > reload
+3. Find "API Explorer" in local apps, install and start
+4. Open via the sidebar panel
+
+## Architecture
+
+The app runs a lightweight aiohttp Python server inside an HA base container with s6-overlay. The browser cannot reach `http://supervisor` directly (it's Docker-internal), so the app server acts as a proxy for API calls.

api_explorer/build.yaml

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+---
+build_from:
+  aarch64: ghcr.io/home-assistant/aarch64-base-python:3.13-alpine3.21
+  amd64: ghcr.io/home-assistant/amd64-base-python:3.13-alpine3.21

api_explorer/config.yaml

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+name: API Explorer
+version: "1.0.0"
+slug: api_explorer
+description: Inspect ingress headers and test Home Assistant Core API calls through Supervisor
+url: https://www.home-assistant.io
+arch:
+  - amd64
+  - aarch64
+ingress: true
+ingress_port: 8099
+panel_icon: mdi:api
+panel_title: API Explorer
+homeassistant_api: true
+init: false
+startup: application
+boot: manual