fix(cli): wire /indicator slash command to a handler

[luyao618]

Summary

Fixes #27603. The /indicator slash command was declared in hermes_cli/commands.py COMMAND_REGISTRY (with subcommands kaomoji|emoji|unicode|ascii) and shows up in autocomplete/help, but HermesCLI.process_command() in cli.py had no matching elif canonical == "indicator" branch. As a result, typing /indicator unicode fell through to the "Unknown command" path even though the command is documented and the underlying config key (display.tui_status_indicator) is fully supported by the TUI gateway and ui-tui consumers.

What changed

• cli.py
  • process_command() now dispatches canonical == "indicator" to a new handler, placed next to the existing /skin and /busy handlers.
  • _handle_indicator_command() mirrors the style of _handle_busy_command():
    • /indicator or /indicator status → prints the current style (read from load_cli_config() → display.tui_status_indicator, defaulting to kaomoji) and usage hint.
    • /indicator <kaomoji|emoji|unicode|ascii> → validates the arg, calls save_config_value("display.tui_status_indicator", arg), and prints a confirmation. Unknown args get a usage hint and no write.
• tests/hermes_cli/test_indicator_command.py (new)
  • Asserts indicator is present in COMMAND_REGISTRY and resolves via resolve_command().
  • Asserts HermesCLI._handle_indicator_command exists and that process_command() source contains the dispatch branch (regression guard for the original bug).
  • Calls the handler directly with a valid style and asserts save_config_value is invoked with the right key/value.
  • Calls the handler with a bogus style and asserts nothing is persisted.

Verification

• The display.tui_status_indicator config key already exists (hermes_cli/config.py:1006, default kaomoji) and is consumed by tui_gateway/server.py and ui-tui/src/app/useConfigSync.ts, so this change just exposes the existing knob via the slash command users were already trying to type.
• The original issue body referenced display.busy_indicator_style; verified the real key in this repo is display.tui_status_indicator and used that.
• pytest tests/hermes_cli/test_indicator_command.py -x -q → 4 passed.

Risk

Very low. Pure additive change:

• New elif branch in command dispatch — does not affect other commands.
• New method on HermesCLI.
• New test file.

No changes to behavior of any other slash command or to the config-key semantics.

[alt-glitch]

Fixes #27603 (duplicate of #22960). Note: competing PRs #22962, #23006, #22965, #23289 were all closed without merging for the same fix.

[luyao618]

Closing — 4 prior PRs for the same #22960/#27603 fix (#22962, #23006, #22965, #23289) were all closed without merging, so this route clearly isn't being accepted. Not worth keeping another one open.