fix(issue-26): the wrapper reads .mam.env through the Python loader's parser, never source

- lib_py/delegation/envfile.py (stdlib only) holds the one set of rules:
  comments and blank lines skipped, key and value stripped, one matching
  quote pair removed, no shell interpretation, keys must match
  ^[A-Za-z_][A-Za-z0-9_]*$ (bad or `=`-less lines warn with the line
  number, never the value).
- mqtt_common._parse_env_file delegates to envfile.apply.
- The delegate-job wrapper runs envfile.py --shell by path and evals the
  shlex-quoted exports; values never reach a command line. The environment
  now wins over the file in both loaders.
- .mam.env.example: commented assignments no longer use $HOME, which the
  parser keeps literally.

The shell parsed the env file in one place only (wrapper :38), not three.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.mam.env.example

@@ -29,11 +29,11 @@
 
 # Root directory that holds Claude Code per-project conversation logs (*.jsonl).
 #default: $HOME/.claude/projects
-# CLAUDE_PROJECT_DIR=$HOME/.claude/projects
+# CLAUDE_PROJECT_DIR=/home/you/.claude/projects
 
 # Directory scanned for per-session launcher wrappers (~/.local/bin/<session>).
 #default: $HOME/.local/bin
-# LOCAL_BIN=$HOME/.local/bin
+# LOCAL_BIN=/home/you/.local/bin
 
 # Isolated Herdr session socket name (`herdr --session <name>`).
 #default: mam-<workspace-slug>
@@ -46,7 +46,7 @@
 
 # Path to the Herdr Unix domain socket.
 #default: $HOME/.config/herdr/herdr.sock
-# HERDR_SOCKET_PATH=$HOME/.config/herdr/herdr.sock
+# HERDR_SOCKET_PATH=/home/you/.config/herdr/herdr.sock
 
 # Explicit Herdr workspace scope identifier (`herdr pane list --workspace <id>`).
 # Hard filters pane/agent resolution to this workspace. When unset, falls back
@@ -107,7 +107,7 @@
 
 # Optional override for Codex CLI state / session directory.
 #default: $HOME/.codex
-# CODEX_HOME=$HOME/.codex
+# CODEX_HOME=/home/you/.codex
 
 # Optional inline JSON permissions configuration for OpenCode.
 #default: (unset → defaults to --auto CLI bypass)