oraclemcp P1-6: connect/list_profiles + login scripts + allow-once token

Bead oracle-qmwz.2.6. oraclemcp-core::connect.build_session_context maps a
named profile -> OracleConnectOptions + SessionLevelState (ceiling, standby
forces READ_ONLY) + ordered login statements (canonical NLS + read-only
backstop + operator login script). oraclemcp-guard::token.AllowOnceStore: a
single-use, SQL-digest-bound, monotonic-TTL token documented as friction (NOT a
security control). list_profiles is config.list_profiles (secret-free).
8 tests; clippy -D warnings + fmt clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Durak