feat(setup): auto-reconfigure on existing installs (#15879)

Bare `hermes setup` on a returning user now drops straight into the
full reconfigure wizard — every prompt shows the current value as its
default, press Enter to keep or type a new value to change it. The
returning-user menu is gone.

Behavior:
- First-time user: first-time wizard (unchanged)
- Returning user, bare command: full reconfigure wizard (new default)
- Returning user, `--quick`: only prompt for missing/unset items
- Returning user, one section: `hermes setup model|terminal|gateway|tools|agent`
- `--reconfigure`: preserved as backwards-compat alias (no-op since it's now default)

The section functions already used current values as prompt defaults —
this change just removes the extra click to get to them.

The 'Quick Setup - configure missing items only' menu option is now
exposed as the explicit `--quick` flag; it's the narrow case of
filling in missing config (e.g. after a partial OpenClaw migration or
when a required API key got cleared).

Inspired by Mercury Agent's `mercury doctor` UX.

Also removes:
- RETURNING_USER_MENU_SECTION_KEYS (orphaned constant)
- Two returning-user menu tests in test_setup_noninteractive.py
  (guarding behavior that no longer exists — covered by
  test_setup_reconfigure.py instead)

hermes_cli/main.py

@@ -7734,6 +7734,19 @@ For more help on a command:
     setup_parser.add_argument(
         "--reset", action="store_true", help="Reset configuration to defaults"
     )
+    setup_parser.add_argument(
+        "--reconfigure",
+        action="store_true",
+        help="(Default on existing installs.) Re-run the full wizard, "
+             "showing current values as defaults. Kept for backwards "
+             "compatibility — a bare 'hermes setup' now does this.",
+    )
+    setup_parser.add_argument(
+        "--quick",
+        action="store_true",
+        help="On existing installs: only prompt for items that are missing "
+             "or unset, instead of running the full reconfigure wizard.",
+    )
     setup_parser.set_defaults(func=cmd_setup)
 
     # =========================================================================