feat(onboard): user onboarding - no default USER.md, guided creation (#37)

- bootstrap no longer creates user/USER.md (owner direction)
- scripts/onboard.sh: name REQUIRED (interactive loop or --name),
  optional fields prompted (profession, marital, age, gender, education,
  location, timezone, skillset, interests, hobbies, pets); flag-driven
  non-interactive mode for automation
- templates/USER.md: canon skeleton, placeholder rendering, unfilled
  optional = (not provided)
- agent.sh: auto-runs onboarding when profile missing (TTY gate);
  headless run-task warns and continues without user context
- user profile dispatched to all launches (M14 layer)

Closes #37 (onboarding requirements from owner layout review)

scripts/common.sh

@@ -50,11 +50,8 @@ bootstrap_runtime_dir() {
         echo "bootstrap: created $MOSAIC_DEV_DIR"
     fi
     touch "$MOSAIC_DEV_DIR/$POC_ROOT_MARKER"
-    # Live user context layer (M14): seeded once, owned by the user from
-    # then on; dispatched to every agent launch without rebuilds.
+    # Live user context layer (M14/M16): the directory is system-managed,
+    # but USER.md is NEVER auto-created. Onboarding (scripts/onboard.sh,
+    # auto-invoked by agent.sh) creates it from the template.
     mkdir -p "$MOSAIC_DEV_DIR/user"
-    if [ ! -f "$MOSAIC_DEV_DIR/user/USER.md" ]; then
-        printf '# User\n\nDescribe yourself, your machine, and your preferences here.\nThis file is dispatched to every Mosaic agent launch.\n' \
-            > "$MOSAIC_DEV_DIR/user/USER.md"
-    fi
 }