feat(tui): port classic CLI /reload (.env hot-reload) to TUI

Classic CLI exposes ``/reload`` (re-reads ~/.hermes/.env into
``os.environ`` via ``hermes_cli.config.reload_env``) so newly added API
keys take effect without restarting the session.  The TUI was missing
the parity command, so users had to Ctrl+C out and ``hermes --tui``
again whenever they added or rotated a credential.

Three small wires:

* New ``reload.env`` JSON-RPC method in ``tui_gateway/server.py`` that
  delegates to ``hermes_cli.config.reload_env`` and returns the count
  of vars updated.
* New ``/reload`` slash command in ``ui-tui/src/app/slash/commands/ops.ts``
  matching the existing ``/reload-mcp`` pattern (native RPC, no slash
  worker).
* Drop ``cli_only=True`` from the ``reload`` ``CommandDef`` in
  ``hermes_cli/commands.py`` so help/menus surface it in the TUI too.
  ``reload_env`` itself is environment-agnostic.

Same caveat as classic CLI: the *currently constructed* agent's
credential pool / provider routing does not auto-rebuild.  Users who
want a brand-new credential resolution should follow with ``/new``.

Tests:
* New ``test_reload_env_rpc_calls_hermes_cli_reload_env`` confirms
  RPC delegates and reports the count.
* New ``test_reload_env_rpc_surfaces_errors`` confirms exceptions are
  rendered as JSON-RPC errors.
* ``createSlashHandler.test.ts`` slash-parity matrix extended with
  ``['/reload', 'reload.env', {}]`` so we can't regress the routing.

Validation:
  scripts/run_tests.sh tests/test_tui_gateway_server.py — 92/92.
  scripts/run_tests.sh tests/hermes_cli/test_commands.py — 128/128.
  cd ui-tui && npm run type-check — clean; npm test --run — 390/390.

hermes_cli/commands.py

@@ -148,8 +148,7 @@ COMMAND_REGISTRY: list[CommandDef] = [
     CommandDef("cron", "Manage scheduled tasks", "Tools & Skills",
                cli_only=True, args_hint="[subcommand]",
                subcommands=("list", "add", "create", "edit", "pause", "resume", "run", "remove")),
-    CommandDef("reload", "Reload .env variables into the running session", "Tools & Skills",
-               cli_only=True),
+    CommandDef("reload", "Reload .env variables into the running session", "Tools & Skills"),
     CommandDef("reload-mcp", "Reload MCP servers from config", "Tools & Skills",
                aliases=("reload_mcp",)),
     CommandDef("browser", "Connect browser tools to your live Chrome via CDP", "Tools & Skills",