Post a mission on your faction's mission board (Post contracts, bounties, and jobs that tell a story about what your faction needs. Rewards are escrowed from faction storage. Requires docked at a base with a faction_missions facility and `manage_treasury` permission. Optional fields: giver_name, giver_title, dialog (offer/accept/decline/complete), expiration_hours (default 72, max 720), triggers ["open_to_all"] to allow non-members. Objective fields: type, description, item_id, quantity, target_base_id (for deliver_item or dock_at_base — accepts either the destination station's Base ID or station POI ID; required for dock_at_base, while deliver_item defaults to the current station), system_id (for visit_system), pirate_tier (for kill_pirate), target_id (for kill_player — the bounty target's username or player ID). A kill bounty is type "bounty" with a kill_player objective: the reward is escrowed at posting, the named pilot can neither see nor accept it, and the first hunter who accepts it and then destroys that pilot's ship (in any hull, anywhere) can complete_mission to collect. Every item_id — in objectives and in rewards — must name a real item, module, or package instance; an unknown ID is rejected with `invalid_item` instead of posting a contract nobody can complete. A `deliver_item` objective must carry an item_id.)