feat(terminal): tint terminal background per agent color

Add backend-agnostic terminal color support via OSC escape sequences:
- New backend/terminal.py with palette_printf() and exec_shell_script()
  shared by both Docker and smolmachines bottle backends
- Emits OSC 4 (indexed palette) + OSC 11 (default background tint)
  before launching; resets both on agent exit via OSC 104/111
- OSC 11 background tint is visible even when the TUI uses true/24-bit
  colors (which bypass the palette), as Codex does for its chrome
- Fix Codex [tui] config: status_line=["model-with-reasoning"],
  theme="ansi" (dark-ansi and cwd/directory were invalid identifiers)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bot_bottle/contrib/codex/agent_provider.py

@@ -104,9 +104,9 @@ class CodexAgentProvider(AgentProvider):
             'trust_level = "trusted"\n'
             "\n"
             "[tui]\n"
-            'status_line = ["model", "cwd"]\n'
+            'status_line = ["model-with-reasoning"]\n'
             'terminal_title = ["spinner", "project"]\n'
-            'theme = "dark-ansi"\n'
+            'theme = "ansi"\n'
         )
         config_file.chmod(0o600)
         files.append(AgentProvisionFile(config_file, config_path))