fix(config): wire up LLM_PROXY__CONFIG_PATH env var and fix database path in service

The app never read the LLM_PROXY__CONFIG_PATH env var, so the systemd
service couldn't find /etc/llm-proxy/config.toml and fell back to
./data/llm_proxy.db (owned by root, readonly for llmproxy user).

- Add LLM_PROXY__CONFIG_PATH support to config loader (checks env var
  before falling back to ./config.toml)
- Add LLM_PROXY__DATABASE__PATH to service env so the DB path always
  resolves to /var/lib/llm-proxy/llm_proxy.db regardless of config

deploy.sh

@@ -264,6 +264,7 @@ WorkingDirectory=$INSTALL_DIR
 EnvironmentFile=$ENV_FILE
 Environment="RUST_LOG=info"
 Environment="LLM_PROXY__CONFIG_PATH=$CONFIG_DIR/config.toml"
+Environment="LLM_PROXY__DATABASE__PATH=$DATA_DIR/llm_proxy.db"
 ExecStart=$INSTALL_DIR/target/release/$APP_NAME
 Restart=on-failure
 RestartSec=5

src/config/mod.rs

@@ -139,7 +139,10 @@ impl AppConfig {
             .set_default("providers.ollama.models", Vec::<String>::new())?;
 
         // Load from config file if exists
-        let config_path = config_path.unwrap_or_else(|| {
+        // Priority: explicit path arg > LLM_PROXY__CONFIG_PATH env var > ./config.toml
+        let config_path = config_path
+            .or_else(|| std::env::var("LLM_PROXY__CONFIG_PATH").ok().map(PathBuf::from))
+            .unwrap_or_else(|| {
                 std::env::current_dir()
                     .unwrap_or_else(|_| PathBuf::from("."))
                     .join("config.toml")