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/scripts/prompt.template.md

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+# Bird illustration prompt
+
+This is the prompt sent to Gemini for every bird illustration. Edit it
+to change the style — the entire visual feel of the collage flows
+through this template.
+
+Two placeholders get replaced per request:
+
+- `{sci_name}` — the binomial Latin name, e.g. `Calypte anna`
+- `{com_name}` — the English common name, e.g. `Anna's Hummingbird`
+- `{pose}` — either `perched` (pose 1) or `in flight with wings spread` (pose 2)
+
+The default style below is **kachō-e** — Edo-period Japanese
+flower-and-bird woodblock prints, rendered in ink and watercolor on
+warm paper. Replace the body of the prompt with whatever feels right
+for your apartment.
+
+---
+
+## Prompt
+
+Generate a {pose} {com_name} ({sci_name}) in the style of an Edo-period
+Japanese kachō-e woodblock print. Confident sumi-e ink linework with
+soft watercolor washes. Earthy, restrained palette — burnt umber,
+ochre, indigo, vermillion, muted greens. Plumage details rendered with
+short directional brush strokes; eye, beak, and feet drawn with crisp
+ink. The bird should be the only subject — NO background, NO branch
+unless the pose requires it (a single sparse twig is fine for
+perched), NO border or frame, NO text or signature.
+
+Anatomy must be biologically accurate for the named species:
+
+- Exactly two wings. Two legs. One head. One beak. One tail.
+- Posture and feather pattern matching {com_name} field-guide
+  references — color, markings, and body proportions must match the
+  real bird.
+- For perched poses: one wing folded against the body, the other
+  tucked behind. For flight: both wings extended in a natural flapping
+  position.
+
+Render at high resolution on a clean transparent background. Output
+the illustration with no surrounding scene, no caption, no shadow
+beneath the bird.