AvianVisitors: BirdNET-Pi collage frontend overlay

Adds avian/ on top of upstream BirdNET-Pi:
- frontend/    static collage UI (mask-packed bird tiles, sized by detection count)
- assets/      ~450 bundled kachō-e illustrations + cutouts + binary masks
- api/         PHP shims for recent/lifelist/firstseen/timeseries JSON
- scripts/     installer + Gemini pregen + editable prompt template
- caddy/       snippet mounting /collage on existing Caddy
- forwarding/  optional HA / MQTT / Cloudflare configs

Default install: http://birdnet.local/collage/ with no auth.

Upstream BirdNET-Pi README preserved at README.upstream.md.

avian/forwarding/mqtt-bridge.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+"""Poll /api/recent.json on the Pi once a minute and publish each new
+detection to MQTT. Edit BROKER, TOPIC_PREFIX, and PI_URL below."""
+import json
+import time
+import urllib.request
+import paho.mqtt.client as mqtt  # sudo pip3 install paho-mqtt
+
+BROKER = "homeassistant.local"
+PORT = 1883
+USER = ""
+PASSWORD = ""
+TOPIC_PREFIX = "birdnet"
+PI_URL = "http://birdnet.local/api/recent.json?hours=1"
+
+seen_keys: set[str] = set()
+
+def slugify(s: str) -> str:
+    return "".join(c.lower() if c.isalnum() else "-" for c in s).strip("-")
+
+def loop(client: mqtt.Client) -> None:
+    while True:
+        try:
+            with urllib.request.urlopen(PI_URL, timeout=10) as r:
+                payload = json.loads(r.read())
+            for s in payload.get("species", []):
+                key = f"{s['sci']}|{s.get('last_seen','')}"
+                if key in seen_keys:
+                    continue
+                seen_keys.add(key)
+                topic = f"{TOPIC_PREFIX}/{slugify(s['sci'])}"
+                client.publish(topic, json.dumps(s), qos=0, retain=False)
+                print(f"published {topic}: {s.get('com')}")
+        except Exception as e:
+            print(f"poll error: {e}")
+        time.sleep(60)
+
+def main() -> None:
+    client = mqtt.Client()
+    if USER:
+        client.username_pw_set(USER, PASSWORD)
+    client.connect(BROKER, PORT, keepalive=60)
+    client.loop_start()
+    loop(client)
+
+if __name__ == "__main__":
+    main()