fix: interactive Realm password, recoverable worker budget (0.9.15)

Prompt for Realm password when CST_REALM_PASSWORD is unset; map worker
request-gate exhaustion to a clear budget error with partial progress;
hard-skip identical tool failures after 3 tries. Add docs/parliament.md.

Co-authored-by: Cursor <cursoragent@cursor.com>

include/cst_agent.h

@@ -477,6 +477,8 @@ int cst_creds_resolve(const char *provider, char *out, size_t out_sz,
                       const char **from);
 /* Hidden console prompt (no echo). */
 int cst_creds_prompt_console(const char *provider, char *out, size_t out_sz);
+/* Generic hidden prompt for passwords / secrets (TTY only). */
+int cst_prompt_secret(const char *prompt, char *out, size_t out_sz);
 
 /* Last used provider, model per provider, effort and working mode, in
  * <config>/settings.json. */