fix(cli): clamp curses color 8 for 8-color terminals (Docker)

curses.init_pair(N, 8, -1) uses extended color 8 ("bright black" /
dim gray) which does not exist on 8-color terminals (COLORS == 8,
valid range 0-7).  This crashes the entire plugins UI, session
browser, and radio picker in Docker containers with:

    curses.error: init_pair() : color number is greater than COLORS-1

Replace all 5 occurrences across plugins_cmd.py, main.py, and
curses_ui.py with min(8, curses.COLORS - 1), which falls back to
COLOR_WHITE (7) on 8-color terminals.

Closes #13688

hermes_cli/curses_ui.py

@@ -71,7 +71,7 @@ def curses_checklist(
                 curses.use_default_colors()
                 curses.init_pair(1, curses.COLOR_GREEN, -1)
                 curses.init_pair(2, curses.COLOR_YELLOW, -1)
-                curses.init_pair(3, 8, -1)  # dim gray
+                curses.init_pair(3, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)  # dim gray
             cursor = 0
             scroll_offset = 0