fix(auth): restore env-var overrides for scope, redirect URI, and response type

Upstream hardcoded these values in 1.0.87+; restore os.environ.get() wrappers
so deployments can override without code changes. Default scope keeps
ads_management and ads_read on top of upstream's narrowed set.

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

Author: mdrokon-dev

meta_ads_mcp/core/auth.py

@@ -25,9 +25,9 @@
 # Auth constants
 # Scope includes pages_show_list and pages_read_engagement to fix issue #16
 # where get_account_pages failed for regular users due to missing page permissions
-AUTH_SCOPE = "business_management,public_profile,pages_show_list,pages_read_engagement"
-AUTH_REDIRECT_URI = "http://localhost:8888/callback"
-AUTH_RESPONSE_TYPE = "token"
+AUTH_SCOPE = os.environ.get("META_AUTH_SCOPE", "ads_management,ads_read,business_management,public_profile,pages_show_list,pages_read_engagement")
+AUTH_REDIRECT_URI = os.environ.get("META_REDIRECT_URI", "http://localhost:8888/callback")
+AUTH_RESPONSE_TYPE = os.environ.get("META_AUTH_RESPONSE_TYPE", "token")
 
 # Log important configuration information
 logger.info("Authentication module initialized")