agents create: expose spec-backed turn/prompt knobs as first-class flags

[longevityboris]

Context

Flagged by Codex audit (docs/reference/spec-audit-pre-v0.3.0.md §4). We documented these as patch-only paths in AGENTS_UPDATE_HELP but they're common enough that PATCHing for every tweak is friction.

Candidates (spec-backed, high-signal)

TurnConfig

• --initial-wait-time <secs> → conversation_config.turn.initial_wait_time
• --silence-end-call-timeout <secs> → conversation_config.turn.silence_end_call_timeout (−1 disables)
• --soft-timeout-secs <secs> + --soft-timeout-message <str> → conversation_config.turn.soft_timeout_config
• --turn-mode <silence|turn> → conversation_config.turn.mode

PromptAgentAPIModel

• --reasoning-effort <none|minimal|low|medium|high|xhigh> → prompt.reasoning_effort
• --max-tokens <n> → prompt.max_tokens
• --thinking-budget <n> → prompt.thinking_budget
• --ignore-default-personality → prompt.ignore_default_personality
• --rag / --rag-max-chunks <n> → prompt.rag.*

AgentConfig

• --max-duration-message <str> → agent.max_conversation_duration_message (what the agent says when hitting the hard timeout)

Use case

Every one of these was a PATCH in the user's Guidance 40 session. Turning them into flags cuts the work from "PATCH roundtrip + rebuild the body" to one line.

Files

• src/cli.rs (AgentsAction::Create)
• src/commands/agents/create.rs
• src/commands/agents/mod.rs (dispatch)
• src/help.rs (AGENTS_CREATE_HELP, AGENTS_UPDATE_HELP)
• src/commands/agent_info.rs

Acceptance

• Each flag writes to the spec-correct path.
• Enum-valued flags use clap value_parser! with the spec enum.
• AGENTS_UPDATE_HELP keeps the patch-path documentation (patching should still work).