Add configuration loading and error handling

Introduces a new `config` module for loading application settings from
environment variables and a `users.toml` file. An `error` module is
added to handle application-specific errors gracefully. An
`.env.example` file is created to show available configuration options,
and `users.toml.example` provides a template for user data. The main
function now initializes the configuration and prints the server port.

server/.env.example

@@ -0,0 +1,33 @@
+# === Required (Phase 1) ===
+
+SERVER_PORT=3000
+DATA_PATH=/data
+USERS_FILE=users.toml
+LOG_LEVEL=info
+LOG_PATH=/var/log/recorder
+LOG_MAX_DAYS=90
+
+# === Optional (Phase 2+) ===
+
+# Retention
+RETENTION_AUDIO_DAYS=30
+RETENTION_TRANSCRIPT_DAYS=30
+RETENTION_DOCUMENT_DAYS=0
+
+# faster-whisper
+WHISPER_URL=http://localhost:10300
+WHISPER_TIMEOUT_SECONDS=120
+
+# Ollama
+OLLAMA_URL=http://localhost:11434
+OLLAMA_MODEL=gemma3:4b
+OLLAMA_KEEP_ALIVE=0
+
+# LLM provider (Ionos)
+LLM_URL=https://openai.ionos.com/openai
+LLM_API_KEY=
+LLM_MODEL=
+LLM_TEMPERATURE=0
+
+# Session
+SESSION_TIMEOUT_HOURS=8