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

website/docs/user-guide/tui.md

@@ -36,7 +36,16 @@ hermes          # now uses the TUI
 hermes chat     # same
 ```
 
-The classic CLI remains available as the default. Anything documented in [CLI Interface](cli.md) — slash commands, quick commands, skill preloading, personalities, multi-line input, interrupts — works in the TUI identically.
+Or make it the persistent default in `~/.hermes/config.yaml`:
+
+```yaml
+display:
+  interface: tui   # "cli" (default) or "tui"
+```
+
+With `display.interface: tui`, a bare `hermes` (and `hermes chat`) launches the TUI. Explicit flags always win — run `hermes --cli` to drop back to the classic REPL for a single invocation, or `hermes --tui` / `HERMES_TUI=1` to force the TUI when the config default is `cli`.
+
+The classic CLI remains the shipped default. Anything documented in [CLI Interface](cli.md) — slash commands, quick commands, skill preloading, personalities, multi-line input, interrupts — works in the TUI identically.
 
 ## Why the TUI
 
@@ -283,7 +292,7 @@ This is the same channel the web dashboard's embedded TUI uses (see [Web Dashboa
 
 ## Reverting to the classic CLI
 
-Launching `hermes` (without `--tui`) stays on the classic CLI. To make a machine prefer the TUI, set `HERMES_TUI=1` in your shell profile. To go back, unset it.
+Launching `hermes` (without `--tui`) stays on the classic CLI by default. To make a machine prefer the TUI, set `display.interface: tui` in `~/.hermes/config.yaml` (persistent) or `HERMES_TUI=1` in your shell profile (per-shell). To go back, set `interface: cli` / unset the env var, or pass `hermes --cli` for a one-off.
 
 If the TUI fails to launch (no Node, missing bundle, TTY issue), Hermes prints a diagnostic and falls back — rather than leaving you stuck.