AvianVisitors hardening pass — install via fork's newinstaller

Restructures the install so users run ONE command. The fork's
newinstaller.sh clones this repo (instead of upstream Nachtzuster) and
runs BirdNET-Pi's installer. install_services.sh symlinks the avian/
overlay into the Caddy site root, so http://birdnet.local/avian/ comes
up after reboot with no Caddy config needed.

Reviewer-flagged fixes:

Frontend (avian/frontend/apt.js)
- Switch all API paths from /api/*.json (which didn't route) to relative
  action-based URLs (./api/birdnet-api.php?action=recent etc.).
- Fetch ./masks.json + ./dims.json relatively (were /avian/*.json).
- Replace every innerHTML user-content sink with createElement +
  textContent + setAttribute — species labels are user-editable in
  BirdNET-Pi, so untrusted.
- Add esc() helper for the few remaining innerHTML attribute contexts.
- fetchJson throws on non-200 (was silently parsing 404 HTML as JSON).
- Defensive null-check in loadMask if MASKS hasn't loaded.

Backend (avian/api/*.php)
- birdnet-api.php now derives DB_PATH from dirname(__DIR__, 3) so any
  BirdNET-Pi install user works (no hardcoded /home/birdnet).
- recording/spectrogram/cutout use getenv('HOME') for the same reason.
- cutout.php reworked as the canonical image resolver: bundled
  illustration → bundled cutout → cached rembg → fresh
  Wikipedia+rembg, with the binomial regex guard and atomic rename
  on cache write. Wikipedia URL host pinned to wikimedia.org /
  wikipedia.org to block SSRF.
- Stale 'X-BirdNET-Proxy-Token' auth claims removed everywhere.

Pregen (avian/scripts/pregen.py)
- Gemini key moved from URL query to x-goog-api-key header.
- Model bumped to gemini-2.5-flash-image-preview.
- Bounded retry on 429 + 5xx with Retry-After honoured.
- Default --sleep raised from 1s to 4s (under free-tier RPM).
- Unified parser handles |/_/comma in all three input modes.
- responseModalities now [TEXT, IMAGE] (was IMAGE-only).
- --poses validated against POSES keys.
- ASCII [ok]/[fail] markers (was ✓/✗ — Windows console crash).
- Surfaces finishReason + blockReason on safety blocks.

Prompt template
- 'Two placeholders' typo → three.
- 'warm paper' / 'transparent background' contradiction resolved.

Forwarding
- mqtt-bridge.py: paho-mqtt 2.x CallbackAPIVersion compat shim.
- avian-mqtt.service: dropped broken %i, set User=birdnet + %h path.
- forwarding/README.md uses the actual action-based URLs.

README
- One-line install via curl … newinstaller.sh.
- No more 'install BirdNET-Pi separately' step (our fork does it).
- License section uses absolute github.com links.
- bird.onethreenine.net replaces the not-yet-existent project writeup.
- docs/thumb.png replaced with the 24-bird Twitter capture.

Removed
- avian/caddy/ and avian/scripts/install.sh — no longer needed; the
  overlay symlink in install_services.sh handles everything.

avian/api/spectrogram.php

@@ -1,8 +1,8 @@
 <?php
-// /home/monalisa/BirdSongs/Extracted/spectrogram.php — serves the
-// spectrogram PNG that BirdNET-Pi generates alongside each detection mp3.
-// Same lookup logic as recording.php (find the matching file under
-// By_Date/<date>/<Common_Name>/) — just .png instead of .mp3.
+// AvianVisitors — serves the spectrogram PNG that BirdNET-Pi generates
+// alongside each detection mp3. Same lookup logic as recording.php (find
+// the matching file under By_Date/<date>/<Common_Name>/) — just .png
+// instead of .mp3.
 //
 // Endpoints:
 //   ?sci=<sci_name>            → newest spectrogram for that species
@@ -31,7 +31,7 @@ if ($sci !== '' && !preg_match('/^[A-Za-z]{2,40}(?:[ ][a-z]{2,40}){1,3}$/', $sci
     exit;
 }
 
-$BY_DATE = '/home/monalisa/BirdSongs/Extracted/By_Date';
+$BY_DATE = getenv('HOME') . '/BirdSongs/Extracted/By_Date';
 
 // ---- Direct-by-file lookup ----
 // BirdNET-Pi writes <base>.mp3 and <base>.png next to each other under
@@ -93,7 +93,7 @@ if ($file !== '') {
 }
 
 function resolve_common(string $sci): ?string {
-    $f = '/home/monalisa/BirdNET-Pi/scripts/birds.json';
+    $f = getenv('HOME') . '/BirdNET-Pi/scripts/birds.json';
     if (is_readable($f)) {
         $list = json_decode((string)file_get_contents($f), true);
         if (is_array($list)) {
@@ -107,7 +107,7 @@ function resolve_common(string $sci): ?string {
             }
         }
     }
-    $labels = '/home/monalisa/BirdNET-Pi/model/labels.txt';
+    $labels = getenv('HOME') . '/BirdNET-Pi/model/labels.txt';
     if (is_readable($labels)) {
         foreach (file($labels, FILE_IGNORE_NEW_LINES) as $line) {
             if (strpos($line, '_') !== false) {