feat: password Realm, single-chair login, shared parliament context (0.9.12)

Derive Realm keys from a user password (Argon2id, no private key on disk).
Login claims the sole chair with handover; peers share parliament context;
--new-project clears it. CLI peer/discover helpers and Docker alpine recipe
included; headless empty-answer retries raised for unattended runs.

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

include/cst_agent.h

@@ -497,6 +497,8 @@ typedef struct {
   char effort[16];
   char mode[16];     /* coding | general, "" = not chosen yet */
   char approval[8]; /* "" = not chosen yet */
+  /* legacy_workers | parliament — parliament replaces in-process subagents. */
+  char collaboration[24];
   int show_thinking; /* TUI: Thought blocks start expanded */
   /* workspaces whose .agent/plugins and .agent/mcp.json may run */
   int ntrusted;