refactor(env): streamline Redis configuration and remove deprecated variables

- Consolidated Redis configuration by introducing a single `REDIS_URL` variable for Celery broker, result backend, and app cache.
- Removed deprecated variables related to Firecrawl and Stripe token limits from `.env.example` files.
- Updated documentation to reflect changes in environment variable usage for improved clarity and maintainability.

docker/.env.example

@@ -185,7 +185,6 @@ STRIPE_PAGE_BUYING_ENABLED=FALSE
 # STRIPE_TOKEN_BUYING_ENABLED=FALSE
 # STRIPE_PREMIUM_TOKEN_PRICE_ID=price_...
 # STRIPE_CREDIT_MICROS_PER_UNIT=1000000
-# DEPRECATED: STRIPE_TOKENS_PER_UNIT=1000000
 
 # ------------------------------------------------------------------------------
 # TTS & STT (Text-to-Speech / Speech-to-Text)
@@ -340,9 +339,6 @@ STT_SERVICE=local/base
 # External API Keys (optional)
 # ------------------------------------------------------------------------------
 
-# Firecrawl (web scraping)
-# FIRECRAWL_API_KEY=
-
 # Unstructured (if ETL_SERVICE=UNSTRUCTURED)
 # UNSTRUCTURED_API_KEY=
 
@@ -418,7 +414,6 @@ SURFSENSE_ENABLE_DOOM_LOOP=true
 # Premium turns are debited at the actual per-call provider cost reported
 # by LiteLLM. Only applies to models with billing_tier=premium.
 # PREMIUM_CREDIT_MICROS_LIMIT=5000000
-# DEPRECATED: PREMIUM_TOKEN_LIMIT=5000000
 
 # Safety ceiling on per-call premium reservation, in micro-USD ($1.00 default).
 # QUOTA_MAX_RESERVE_MICROS=1000000