M1: backend core + proposal engine

- FastAPI skeleton, SQLAlchemy models (§13), Alembic initial migration
- SchedulingProvider interface with google_calendar (free/busy read-only),
  partner_api (Appendix B client) and mock implementations
- Proposal engine: create → provider-routed delivery → owner actions
  (resolve/confirm+SMS/reject) → expiry + reminders (§9)
- Signed single-use action links, .ics METHOD:REQUEST attachment
- Partner outcome webhook with HMAC verification + polling fallback
- SmsProvider (console) with Bosnian templates (§5.5), EmailProvider (console/SMTP)
- Fake partner API server in tests/ — Appendix B reference implementation
- 43 tests: slot math, proposal lifecycle, action links, partner contract

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

gogo/config.py

@@ -0,0 +1,59 @@
+"""Application configuration via environment variables / .env file."""
+
+from functools import lru_cache
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", env_prefix="GOGO_", extra="ignore")
+
+    # Core
+    env: str = "dev"  # dev | test | prod
+    secret_key: str = "dev-secret-change-me"
+    base_url: str = "http://localhost:8000"  # public URL for action links / transcripts
+    database_url: str = "postgresql+psycopg://gogo:gogo@localhost:5432/gogo"
+
+    # Email (SMTP). provider=console logs instead of sending.
+    email_provider: str = "console"  # console | smtp
+    smtp_host: str = "localhost"
+    smtp_port: int = 587
+    smtp_user: str = ""
+    smtp_password: str = ""
+    smtp_starttls: bool = True
+    email_from: str = "Gogo Telefon <noreply@gogotelefon.ba>"
+
+    # SMS. provider=console logs instead of sending (GSM gateway impl in M5).
+    sms_provider: str = "console"  # console | gsm_gateway
+    gsm_gateway_url: str = ""
+    gsm_gateway_user: str = ""
+    gsm_gateway_password: str = ""
+
+    # LLM
+    anthropic_api_key: str = ""
+    llm_model: str = "claude-haiku-4-5-20251001"  # default; per-tenant override possible
+
+    # TTS (decided by Phase-0 PoC; both supported behind TTSProvider)
+    tts_provider: str = "azure"  # azure | elevenlabs
+    azure_speech_key: str = ""
+    azure_speech_region: str = "westeurope"
+    elevenlabs_api_key: str = ""
+
+    # Google OAuth (Calendar free/busy)
+    google_client_id: str = ""
+    google_client_secret: str = ""
+
+    # Proposal engine defaults (overridable per tenant)
+    proposal_ttl_hours: int = 24
+
+    # Retention
+    audio_retention_days: int = 90
+
+    # Session cookies
+    session_cookie: str = "gogo_session"
+    session_max_age: int = 60 * 60 * 24 * 14  # 14 days
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()