[Jackriip]

Survivors you rescue from crashed pods and drifting lifeboats now thank the crew with ship parts.

• On rescue: when the survivor steps aboard, they hand a random ship part (combat, science, trade or misc) to the crew member who brought them in, with a thank-you line. If that person is out of reach or their hands are full, the part goes on the floor.
• Later: every 75–120 minutes the deckhand walks up to a nearby crew member and hands over another part, three more at most. With nobody about, they look again a few minutes later.
• Other strays give nothing.

Numbers: a ship can take 2 strays a round, so at most 8 parts a ship a round (1 on rescue + 3 later, each). Parts still have to go home in an extraction case like any other part. Timing and the cap are defines in voidcrew/_DEFINES/ambient_npcs.dm (AMBIENT_STRAY_GIFT_*).

Built on feature/hyperviolence-mega (#512), where strays are real human NPCs; merge after #512.

Not playtested yet. Compiles clean, and the strays unit tests pass, including new checks for the rescue gift and later gifts.