[feat] roadmap 13 batch C - physics usability + car playability

[AlexZ005]

Batch C - Physics usability + car playability (roadmap #13, lane 1)

C1 - physics discoverability (1edf8be)

• Inspector scene mode gains a Physics section: one row per object that gets a body at sim start (userData.physics + flow Mass overrides, provenance-flagged), row click selects, plus an Enable physics on selection quick action (dynamic mass 1 via the existing objectParameters replication, props undo entries).
• Clearer startSimulation fallback toasts: they say WHY and point at Inspector > Physics.

C2 - angular velocity + motor nodes, torque SDK (0a795ce)

• New Physics flow nodes: angularvelocity (axis + rad/s; setAngvel at sim start, wiring it alone implies dynamic mass 1) and motor (drives every revolute joint touching the selected object, wins over the joint def motor).
• Node param edits re-apply live mid-sim on the stepping peer (change-detected graph subscriptions, cleared on stop).
• api.physics.applyTorqueImpulse(uuid, torque) (initiator-only). NODES.md / MODULES.md updated.
• Sync model: authoritative (initiator applies, motion rides move broadcasts).

C3 - car playability + blow-up ROOT FIX (9751d0a)

• Root cause of the car blow-up found: rapier revolute() takes ONE axis interpreted in BOTH bodies local frames; hull bodies carried the object rotation, so the z-rotated wheel hulls hinged about an axis 90 degrees off the body half and the solver launched the assembly. Hull colliders now bake rotation into their vertices (like scale) so every body starts world-aligned; the hull special-case in the joint anchor math is gone. The car now sits perfectly still and drives upright.
• Play gate: claims work anytime; driving + the chase camera engage only in Play mode with a running sim. Engagement claims keys (kills WASD-flies-camera / pauses play-mode walking) and disengages on exit/release.
• Chase cam via the possess path: chaseCamera() extracted, new camera-only startFollowCam/stopFollowCam + followingCam store.
• Tuning (stable and grippy): FORCE 300->120, MAX_VEL 14->10, STEER_VEL 8->6, wheel friction 1.4->1.1, body mass 20->30, stance 1.15->1.3.

Verification

• New suites: physics-discoverability (11 checks), flow-physics-nodes (two-peer, 10 checks); car-module extended to 16 checks (gate, engagement, chase cam, upright-through-drive).
• physics, physics-kinematic, physics-joints, possess suites green; physics-joints motor phase made robust (wheel hinged in the air + polled read - the grounded layout could contact-lock and stall).
• npm run build green; svelte-check holds the 501/77 baseline on all three commits.

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