fix(cli): make the UI listener switch reachable from config (#1558)

`ui_enabled` governs a loopback HTTP listener on 127.0.0.1:9749, and the only
way to turn it off was hand-editing ~/.cache/codebase-memory-mcp/config.json.
The key was absent from CONFIG_KEYS, so `config list` could not show it and
`config set` rejected it outright. A reporter spent two debugging sessions
finding the switch, and described the surface as looking impossible to turn off.

A network surface a user cannot discover how to disable is not acceptable
whatever its default, and "documented in the source" is not discoverable.

ui_enabled and ui_port now appear in `config list`, and get/set/reset work on
them. They live in a separate file (cbm_ui_config_load/save) rather than the
key-value store the other keys use, so this routes rather than merely listing
them — set validates (true/false; a port in 1..65535) and reports that the
daemon must restart for the change to take effect.

The test asserts DISCOVERABILITY rather than the current values: both keys must
be present in the table that `config list` and `config set` walk, because a key
missing there is a key the user can neither find nor change.

Reported by @PsyTech-Rob.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

src/cli/cli.h

@@ -207,6 +207,10 @@ const char *cbm_cli_clients_token_for_testing(size_t index);
  * not recognisably foreign. Detection must be positive evidence — see the
  * implementation comment. */
 const char *cbm_cli_external_manager_name_for_testing(const char *self_path);
+/* #1558: expose the config-key table so a test can prove a key is discoverable
+ * (`config list`/`set` both walk it). */
+size_t cbm_cli_config_key_count_for_testing(void);
+const char *cbm_cli_config_key_at_for_testing(size_t index);
 #endif
 
 #ifdef CBM_CLI_ENABLE_TEST_API
@@ -410,6 +414,10 @@ int cbm_config_delete(cbm_config_t *cfg, const char *key);
 #define CBM_CONFIG_AUTO_INDEX_LIMIT "auto_index_limit"
 #define CBM_CONFIG_AUTO_WATCH "auto_watch"
 #define CBM_CONFIG_UI_LANG "ui-lang"
+/* #1558: the graph UI's loopback listener. Stored in the UI config file rather
+ * than the key-value store, but surfaced through `config` so it is findable. */
+#define CBM_CONFIG_UI_ENABLED "ui_enabled"
+#define CBM_CONFIG_UI_PORT "ui_port"
 
 /* ── Binary activation safety ─────────────────────────────────── */