fix(nix): unify directory and file permissions across all three layers

Activation script, tmpfiles, and container entrypoint now agree on
0750 for all directories. Tighten config.yaml and workspace documents
from 0644 to 0640 (group-readable, no world access). Add explicit
chmod for .managed marker and container $TARGET_HOME to eliminate
umask dependence. Secrets (auth.json, .env) remain 0600.

nix/nixosModules.nix

@@ -111,6 +111,7 @@
       fi
       mkdir -p "$TARGET_HOME"
       chown "$HERMES_UID:$HERMES_GID" "$TARGET_HOME"
+      chmod 0750 "$TARGET_HOME"
 
       # Ensure HERMES_HOME is owned by the target user
       if [ -n "''${HERMES_HOME:-}" ] && [ -d "$HERMES_HOME" ]; then
@@ -551,8 +552,8 @@
       # ── Directories ───────────────────────────────────────────────────
       {
         systemd.tmpfiles.rules = [
-          "d ${cfg.stateDir}                0755 ${cfg.user} ${cfg.group} - -"
-          "d ${cfg.stateDir}/.hermes        0755 ${cfg.user} ${cfg.group} - -"
+          "d ${cfg.stateDir}                0750 ${cfg.user} ${cfg.group} - -"
+          "d ${cfg.stateDir}/.hermes        0750 ${cfg.user} ${cfg.group} - -"
           "d ${cfg.stateDir}/home           0750 ${cfg.user} ${cfg.group} - -"
           "d ${cfg.workingDirectory}         0750 ${cfg.user} ${cfg.group} - -"
         ];
@@ -566,21 +567,23 @@
           mkdir -p ${cfg.stateDir}/home
           mkdir -p ${cfg.workingDirectory}
           chown ${cfg.user}:${cfg.group} ${cfg.stateDir} ${cfg.stateDir}/.hermes ${cfg.stateDir}/home ${cfg.workingDirectory}
+          chmod 0750 ${cfg.stateDir} ${cfg.stateDir}/.hermes ${cfg.stateDir}/home ${cfg.workingDirectory}
 
           # Merge Nix settings into existing config.yaml.
           # Preserves user-added keys (skills, streaming, etc.); Nix keys win.
           # If configFile is user-provided (not generated), overwrite instead of merge.
           ${if cfg.configFile != null then ''
-            install -o ${cfg.user} -g ${cfg.group} -m 0644 -D ${configFile} ${cfg.stateDir}/.hermes/config.yaml
+            install -o ${cfg.user} -g ${cfg.group} -m 0640 -D ${configFile} ${cfg.stateDir}/.hermes/config.yaml
           '' else ''
             ${configMergeScript} ${generatedConfigFile} ${cfg.stateDir}/.hermes/config.yaml
             chown ${cfg.user}:${cfg.group} ${cfg.stateDir}/.hermes/config.yaml
-            chmod 0644 ${cfg.stateDir}/.hermes/config.yaml
+            chmod 0640 ${cfg.stateDir}/.hermes/config.yaml
           ''}
 
           # Managed mode marker (so interactive shells also detect NixOS management)
           touch ${cfg.stateDir}/.hermes/.managed
           chown ${cfg.user}:${cfg.group} ${cfg.stateDir}/.hermes/.managed
+          chmod 0644 ${cfg.stateDir}/.hermes/.managed
 
           # Seed auth file if provided
           ${lib.optionalString (cfg.authFile != null) ''
@@ -612,7 +615,7 @@ HERMES_NIX_ENV_EOF
 
           # Link documents into workspace
           ${lib.concatStringsSep "\n" (lib.mapAttrsToList (name: _value: ''
-            install -o ${cfg.user} -g ${cfg.group} -m 0644 ${documentDerivation}/${name} ${cfg.workingDirectory}/${name}
+            install -o ${cfg.user} -g ${cfg.group} -m 0640 ${documentDerivation}/${name} ${cfg.workingDirectory}/${name}
           '') cfg.documents)}
         '';
       }