feat: analysis providers, settings UI, song search, WAV duration fix

- Multi-provider AI analysis (Anthropic, OpenAI, Ollama, Algorithmic)
- server-only guards on all provider files; client bundle fix
- /settings page with provider status, Ollama model picker, preferences
- Song search box on /analyze replacing raw MBID input (debounced, keyboard nav)
- Auto-register song via MusicBrainz on POST /api/tracks (no more 404)
- Fix WAV duration bug: last section songEnd was double-counting elapsed time
- Registry sync comment updated for self-hosted HTTPS git servers

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

.env.example

@@ -10,16 +10,33 @@ POSTGRES_PASSWORD=clicktrack
 # ── Redis ────────────────────────────────────────────────────────────────────
 REDIS_URL=redis://localhost:6379
 
-# ── Community registry ───────────────────────────────────────────────────────
+# ── Community registry (optional) ────────────────────────────────────────────
+# HTTPS URL of a git repository containing .ctp.json tempo map files.
+# Compatible with any self-hosted git server (Gitea, Forgejo, GitLab, etc.).
+# To authenticate, embed a personal access token in the URL:
+#   REGISTRY_REPO=https://user:token@git.yourdomain.com/org/clicktrack-registry
 REGISTRY_REPO=
 REGISTRY_BRANCH=main
 REGISTRY_SYNC_INTERVAL=3600
 
 # ── AI Tempo Analysis ────────────────────────────────────────────────────────
-# Required for the /analyze feature (AI tempo map generation).
-# Get a key at https://console.anthropic.com
-# BPM detection is client-side and works without this key.
+# BPM detection is client-side and works without any of these keys.
+
+# --- Cloud AI: Anthropic (existing) ---
+# Required to enable Anthropic provider. Get a key at https://console.anthropic.com
 ANTHROPIC_API_KEY=
+ANTHROPIC_MODEL=claude-opus-4-6  # optional model override
+
+# --- Cloud AI: OpenAI-compatible ---
+OPENAI_API_KEY=                  # required to enable OpenAI provider
+OPENAI_BASE_URL=https://api.openai.com/v1  # override for Groq, Together, Fireworks, etc.
+OPENAI_MODEL=gpt-4o              # optional model override
+
+# --- Local AI: Ollama ---
+OLLAMA_BASE_URL=http://localhost:11434  # required to enable Ollama provider
+# Model is selected by the user in the UI — no OLLAMA_MODEL env var needed
+
+# Algorithmic provider is always available — no config needed.
 
 # ── App ──────────────────────────────────────────────────────────────────────
 NEXT_PUBLIC_APP_NAME=ClickTrack