Add NPC theater poses: sit, photo, film, perform

Once an NPC reaches its intent waypoint it now does something instead of standing
in an idle T-pose:

- sit: the rig settles 0.34 m into a seat and the legs swing forward on the steps
- photo/film: influencers and tourists raise their camera prop briefly (a sine
  pulse, so it reads as taking a shot rather than a permanently raised arm)
- perform: performers sway the sign board they carry

Pose selection lives in NpcAvatar.theater_pose() (intent + arrived); the math is in
pure helpers (crouch_for_pose, prop_lift_for_pose, sway_for_pose) so it is
headless-testable. Prop/leg nodes are captured at build time and animated from
their rest offsets. Performers also get a hand-held board and post.

Tests/docs
- Headless suite 120 -> 127 (test_npc_theater.gd).
- Verified visually with a staged sit/photo/perform lineup in front of the entrance.
- README, TODO section moved to DONE, MEMORY. Version 0.2.7.

DONE.md

@@ -494,3 +494,14 @@ Completed 2026-10-31 (working tree). Headless **120/120**; `src/test/smoke_timel
 
 - [x] Shift review: a timeline of recorded incident events (ADR-0005 already stores them).
       Scrub or step through; no live 3D replay required in the first version.
+
+## NPC theater
+
+Completed 2026-10-31 (working tree). Headless **127/127**; verified visually with a staged sit/photo/perform lineup.
+
+
+Intents `sit` / `photo` / `film` / `perform` already pick waypoints. ADR-0010 rig (face/hair)
+is in the working tree. Bodies still idle-stand at those spots.
+
+- [x] Sit pose at `steps_end`. Photo: brief raise of the influencer/tourist prop. Performer
+      stays put and plays the hat/sign.