fix: correct environment variable names and database config

- Fix environment variable names in compose.yaml:
  * TORRUST_TRACKER_CONFIG_OVERRIDE_CORE__DATABASE__PATH (was URL)
  * TORRUST_TRACKER_CONFIG_OVERRIDE_HTTP_API__ACCESS_TOKENS__ADMIN
- Change database config from 'url' to 'path' in tracker.toml.tpl
- Add comprehensive TOML configuration example in template header
- Replace JSON example with TOML format for consistency
- Update documentation with proper Figment override patterns
- All changes follow torrust-tracker-configuration conventions

These changes ensure the tracker receives correct environment variable
names following the Figment configuration override pattern with
double underscores (__) separating nested sections.

Author: josecelano

application/compose.yaml

@@ -109,10 +109,10 @@ services:
     restart: unless-stopped
     environment:
       - USER_ID=${USER_ID:-1000}
-      # Database connection for tracker
-      - TORRUST_TRACKER_DATABASE_URL=mysql://${MYSQL_USER}:${MYSQL_PASSWORD}@mysql:3306/${MYSQL_DATABASE}
-      # Admin API token for tracker
-      - TORRUST_TRACKER_API_ADMIN_TOKEN=${TRACKER_ADMIN_TOKEN}
+      # Database connection for tracker (using Figment override pattern)
+      - TORRUST_TRACKER_CONFIG_OVERRIDE_CORE__DATABASE__PATH=mysql://${MYSQL_USER}:${MYSQL_PASSWORD}@mysql:3306/${MYSQL_DATABASE}
+      # Admin API token for tracker (using Figment override pattern)
+      - TORRUST_TRACKER_CONFIG_OVERRIDE_HTTP_API__ACCESS_TOKENS__ADMIN=${TRACKER_ADMIN_TOKEN}
     networks:
       - backend_network
     ports:

infrastructure/config/templates/tracker.toml.tpl

@@ -1,5 +1,93 @@
 # Generated Torrust Tracker configuration for ${ENVIRONMENT}
 # Generated on: ${GENERATION_DATE}
+#
+# Configuration Override with Environment Variables:
+# The Torrust Tracker uses the Figment crate for configuration management.
+# Any configuration value can be overridden using environment variables with the pattern:
+# TORRUST_TRACKER_CONFIG_OVERRIDE_<SECTION>__<SUBSECTION>__<KEY>
+#
+# Examples:
+# [core.database]
+# path = "..." -> TORRUST_TRACKER_CONFIG_OVERRIDE_CORE__DATABASE__PATH
+#
+# [http_api.access_tokens]
+# admin = "..." -> TORRUST_TRACKER_CONFIG_OVERRIDE_HTTP_API__ACCESS_TOKENS__ADMIN
+#
+# [logging]
+# threshold = "..." -> TORRUST_TRACKER_CONFIG_OVERRIDE_LOGGING__THRESHOLD
+#
+# Rules:
+# - Use double underscores "__" to separate nested sections/keys
+# - Convert section names to UPPERCASE
+# - Dots in TOML become double underscores in env vars
+# - This follows Figment's environment variable override conventions
+#
+# Example TOML Configuration (output from tracker after merging all sources):
+# [metadata]
+# app = "torrust-tracker"
+# purpose = "configuration"
+# schema_version = "2.0.0"
+# 
+# [logging]
+# threshold = "info"
+# 
+# [core]
+# inactive_peer_cleanup_interval = 120
+# listed = false
+# private = false
+# tracker_usage_statistics = true
+# 
+#   [core.announce_policy]
+#   interval = 120
+#   interval_min = 120
+# 
+#   [core.database]
+#   driver = "sqlite3"
+#   path = "./storage/tracker/lib/database/sqlite3.db"
+# 
+#   [core.net]
+#   external_ip = "0.0.0.0"
+#   on_reverse_proxy = false
+# 
+#   [core.tracker_policy]
+#   max_peer_timeout = 60
+#   persistent_torrent_completed_stat = true
+#   remove_peerless_torrents = true
+# 
+# [[udp_trackers]]
+# bind_address = "0.0.0.0:6868"
+# tracker_usage_statistics = true
+# 
+#   [udp_trackers.cookie_lifetime]
+#   secs = 120
+#   nanos = 0
+# 
+# [[udp_trackers]]
+# bind_address = "0.0.0.0:6969"
+# tracker_usage_statistics = true
+# 
+#   [udp_trackers.cookie_lifetime]
+#   secs = 120
+#   nanos = 0
+# 
+# [[http_trackers]]
+# bind_address = "0.0.0.0:7070"
+# tracker_usage_statistics = true
+# 
+# [[http_trackers]]
+# bind_address = "0.0.0.0:7171"
+# tracker_usage_statistics = true
+# 
+# [http_api]
+# bind_address = "0.0.0.0:1212"
+# 
+#   [http_api.access_tokens]
+#   admin = "***"
+# 
+# [health_check_api]
+# bind_address = "127.0.0.1:1313"
+#
+# Documentation: https://docs.rs/torrust-tracker-configuration/latest/torrust_tracker_configuration/
 
 [metadata]
 app = "torrust-tracker"
@@ -21,8 +109,9 @@ interval_min = 120
 
 [core.database]
 driver = "mysql"
-# URL will be set via environment variable: TORRUST_TRACKER_DATABASE_URL
-url = ""
+# Path will be overridden via environment variable:
+# TORRUST_TRACKER_CONFIG_OVERRIDE_CORE__DATABASE__PATH
+path = ""
 
 [core.net]
 external_ip = "0.0.0.0"
@@ -41,7 +130,8 @@ bind_address = "127.0.0.1:1313"
 [http_api]
 bind_address = "0.0.0.0:1212"
 
-# Admin token will be set via environment variable: TORRUST_TRACKER_API_ADMIN_TOKEN
+# Admin token will be overridden via environment variable:
+# TORRUST_TRACKER_CONFIG_OVERRIDE_HTTP_API__ACCESS_TOKENS__ADMIN
 [http_api.access_tokens]
 # admin = ""