feat(cli): configurable default interface (cli vs tui)

Add `display.interface` config key so users can make the modern TUI the
default for bare `hermes` / `hermes chat` without exporting HERMES_TUI=1 in
every shell. Default stays "cli" to preserve current behavior.

Add a `--cli` flag (mirrors `--tui`) so an explicit invocation can force the
classic prompt_toolkit REPL even when `display.interface: tui` is configured.

Precedence (highest first): `--cli` > `--tui`/`HERMES_TUI=1` > config
`display.interface` > classic REPL. Two resolvers enforce it:

  * `_resolve_use_tui(args)` — the args-aware resolver used by `cmd_chat`
    and the Termux fast-TUI path (uses full load_config()).
  * `_wants_tui_early(argv)` — a dependency-free early resolver used by
    mouse-residue suppression and the Termux fast paths, which run before
    argparse / hermes_cli.config are importable (minimal cached YAML read).

Both `--cli` and `--tui` are registered via `_inherited_flag`, so they are
carried across self-relaunch automatically.

- config: add display.interface ("cli" default), bump _config_version 25->26.
  The generic missing-field migration + load_config() deep-merge seed the key
  for existing configs; no bespoke migration block needed.
- docs: document --cli flag and display.interface in cli-commands.md and
  the TUI user guide.
- tests: new test_default_interface_resolution.py covering resolver
  precedence at every layer, early resolver edge cases (missing/garbage
  config), parser flags, and relaunch inheritance.

website/docs/reference/cli-commands.md

@@ -29,7 +29,8 @@ hermes [global-options] <command> [subcommand/options]
 | `--pass-session-id` | Include the session ID in the agent's system prompt. |
 | `--ignore-user-config` | Ignore `~/.hermes/config.yaml` and fall back to built-in defaults. Credentials in `.env` are still loaded. |
 | `--ignore-rules` | Skip auto-injection of `AGENTS.md`, `SOUL.md`, `.cursorrules`, memory, and preloaded skills. |
-| `--tui` | Launch the [TUI](../user-guide/tui.md) instead of the classic CLI. Equivalent to `HERMES_TUI=1`. |
+| `--tui` | Launch the [TUI](../user-guide/tui.md) instead of the classic CLI. Equivalent to `HERMES_TUI=1`. Always wins over `display.interface`. |
+| `--cli` | Force the classic prompt_toolkit REPL. Use this to override `display.interface: tui` for a single invocation. |
 | `--dev` | With `--tui`: run the TypeScript sources directly via `tsx` instead of the prebuilt bundle (for TUI contributors). |
 
 ## Top-level commands