feat: add NGIT_LOG_LEVEL configuration option

Add proper log level configuration following standard approach:
- CLI flag: --log-level <level>
- Environment variable: NGIT_LOG_LEVEL
- Default: info
- Supports simple levels (error, warn, info, debug, trace)
- Supports filter expressions (e.g., ngit_grasp=debug,actix_web=info)

Configuration is now consistent across all four sources:
1. src/config.rs - Config struct with log_level field
2. docs/reference/configuration.md - Full documentation
3. nix/module.nix - NixOS module with logLevel option
4. .env.example - Example configuration file

This replaces the previous RUST_LOG approach with proper integration
into the ngit-grasp configuration system, enabling trace logging from
CLI, environment variables, or NixOS configuration.

1 files changed, 8 insertions, 3 deletions

diff --git a/nix/module.nix b/nix/module.nix
index 4a6fc94..89d58de 100644
--- a/nix/module.nix
+++ b/nix/module.nix
@@ -127,9 +127,14 @@ let
       };
 
       logLevel = mkOption {
-        type = types.enum [ "trace" "debug" "info" "warn" "error" ];
+        type = types.str;
         default = "info";
-        description = "Logging level for RUST_LOG environment variable";
+        example = "debug";
+        description = ''
+          Logging level for application logging.
+          Can be a simple level (trace, debug, info, warn, error) or a filter expression.
+          Examples: "info", "debug", "ngit_grasp=debug,actix_web=info"
+        '';
       };
 
       syncMaxBackoffSecs = mkOption {
@@ -334,7 +339,7 @@ let
       NGIT_REPOSITORY_BLACKLIST = concatStringsSep "," cfg.repositoryBlacklist;
       NGIT_EVENT_BLACKLIST = concatStringsSep "," cfg.eventBlacklist;
       NGIT_MAX_CONNECTIONS = toString cfg.maxConnections;
-      RUST_LOG = cfg.logLevel;
+      NGIT_LOG_LEVEL = cfg.logLevel;
     } // optionalAttrs (cfg.relayName != null) {
       NGIT_RELAY_NAME = cfg.relayName;
     } // optionalAttrs (cfg.archiveReadOnly != null) {