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.

hermes_cli/config.py

@@ -1283,6 +1283,12 @@ DEFAULT_CONFIG = {
         # behavior of showing tool-call summaries inline.
         "resume_skip_tool_only": True,
         "busy_input_mode": "interrupt",  # interrupt | queue | steer
+        # Which interface bare `hermes` (and `hermes chat`) launches by default:
+        #   "cli" — the classic prompt_toolkit REPL (default, preserves prior behavior)
+        #   "tui" — the modern Ink TUI (same as passing `--tui`)
+        # Explicit flags always win over this setting: `--cli` forces the classic
+        # REPL and `--tui` (or HERMES_TUI=1) forces the TUI regardless of config.
+        "interface": "cli",
         # When true, `hermes --tui` auto-resumes the most recent human-
         # facing session on launch instead of forging a fresh one.
         # Mirrors `hermes -c` muscle memory.  Default off so existing
@@ -2284,7 +2290,7 @@ DEFAULT_CONFIG = {
 
 
     # Config schema version - bump this when adding new required fields
-    "_config_version": 25,
+    "_config_version": 26,
 }
 
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