GenerativeConfig.fromEnv constructor
Reads provider API keys and settings from env.
Keys come from each provider's variable (for example GEMINI_API_KEY,
OPENAI_API_KEY, BFL_API_KEY, ELEVENLABS_API_KEY, SUNO_API_KEY);
FLUVIE_GENERATIVE_CACHE_DIR overrides the cache directory and
FLUVIE_GENERATIVE_OFFLINE (1/true) forces cache-only resolution.
Implementation
factory GenerativeConfig.fromEnv(Map<String, String> env) => GenerativeConfig(
credentials: allCredentialsFromEnv(env),
cacheDir: env['FLUVIE_GENERATIVE_CACHE_DIR'],
offline: _truthy(env['FLUVIE_GENERATIVE_OFFLINE']),
);