Add animated state transitions to catwalk actors

[williamthorsen]

Problem

The catwalk scene currently tears down and rebuilds all Excalibur actors on every CanonicalRunStatus update. This causes visual snapping — the orchestrator teleports between stations, agents appear/disappear instantly, and gates toggle without transition. During a live run, this creates a jarring experience.

Proposed solution

Replace the tear-down-and-rebuild pattern in CatwalkScene.updateStatus() with diff-driven animation dispatch:

1. Actor registry — CatwalkScene maintains references to live actors keyed by identity (orchestrator singleton, agents by ID, gates by station pair, artifacts by composite key)
2. Diff computation — On each status update, compute a CatwalkDiff via the existing diffCatwalkConfig() (already implemented and tested)
3. Animation dispatch — For each diff category, call targeted animation methods on the affected actors:
   • Orchestrator walk: actions.moveTo() slides along the catwalk rail
   • Orchestrator working glow: sine-wave opacity pulse via onPreUpdate
   • Agent state transitions: actions.fade() tweens between opacity levels; working agents pulse
   • Agent deactivation: agents that complete their role fade to low opacity instead of being removed (preserves visual history)
   • Gate open: actions.scaleTo() shrinks gate height to zero over ~300ms
   • Artifact appearance: new artifacts fade in from invisible

Key design decisions

• deactivated agent state: new AgentAnimationState value. Agents that leave the config transition to deactivated (low opacity, no pulse) rather than being killed. This preserves a visual record of which agents participated.
• Sine-wave pulse via onPreUpdate: avoids conflicting with Excalibur's sequential action queue, allowing pulse and movement to run simultaneously.
• Tunable constants: all animation values (DEACTIVATED_OPACITY, pulse ranges, frequency) live in constants/animation.ts for easy visual tuning.

Acceptance criteria

• Orchestrator visually walks between stations (not teleporting) when the active phase changes
• Orchestrator pulses when in working state, stops when idle
• Agent state changes are visible as smooth opacity transitions
• Working agents pulse; deactivated agents fade to low opacity
• Gates animate open (scale Y to 0) rather than toggling visibility
• New artifacts fade in at their station position
• Scene updates smoothly when CanonicalRunStatus changes during a live run
• No increase in entity count when status is unchanged (diff detects no changes)
• All animation timing constants are tunable via constants/animation.ts

Scope exclusions

• Station input/output visual layout (inputs left of divider, outputs right, divider line): the slot: 'input' | 'output' field already exists in the data model and differ; visual positioning is deferred
• Chute animation: not in scope for this issue