feat(shell): add interactive cya shell session (CYA-WP-0007)

Implement the full interactive shell REPL with session persistence,
opt-in capped/redacted shell history, State Hub orientation and
explicit slash-command writes, orchestrator/safety wiring, end-session
learning hooks, weakness hints, docs, and tests.

docs/cya-config.example.toml

@@ -6,4 +6,11 @@ backend = "openrouter"
 model = "anthropic/claude-sonnet-4"
 temperature = 0.3
 max_tokens = 2000
-api_key_env = "OPENROUTER_API_KEY"
+api_key_env = "OPENROUTER_API_KEY"
+
+# Optional interactive shell history context. Off by default.
+# Values are capped/redacted before they enter session context.
+[shell_history]
+enabled = false
+limit = 50
+# histfile = "~/.bash_history"