conversations list: expose the full spec-backed filter set

[longevityboris]

Context

Flagged by Codex audit. get_conversation_histories_route in the OpenAPI spec supports a rich filter set we don't expose. Currently conversations list only accepts --agent-id, --page-size, --cursor.

Spec-backed filters missing

• call_successful (bool)
• has_feedback_comment (bool)
• call_start_after_unix / call_start_before_unix (i64)
• call_duration_secs_min / call_duration_secs_max (u32)
• call_ratings (enum: positive/negative/unknown, repeatable)
• search (free text over transcripts / summaries)
• conversation_initiation_source (enum)
• user_id
• tool_names / tool_names_exclude (repeatable)
• main_languages (repeatable)
• summary_mode (enum: summary/full/none)
• branch_id
• topic_ids (repeatable)

Use case

Debugging voice-agent quality at scale. Current CLI forces users to pull the full list and filter client-side, which falls over on any workspace with >100 conversations.

Files

• src/cli.rs (ConversationsAction::List)
• src/commands/conversations.rs (list fn)
• src/commands/agent_info.rs

Acceptance

• All filters above wired up via --flag syntax.
• Integration test asserts each filter ends up as the matching query param.
• Help text covers the common ones (search / call_successful / call_ratings).