feat(fableloom): add entry, hold-loop, and transition playback assets (#5382)

[atomantic]

Summary

Implements entry clips, hold-loop variations, transition-specific exits, and audio-occupancy validation for FableLoom interactive narratives (part of #5377).

• Backward-Compatible Asset Model: Retains legacy videoHistoryId fallback while introducing playbackAssets (entryVideoHistoryId, holdLoopVideoHistoryIds, exitByTransition, audioOccupancy, provenance) and interactionWindow (enabled, protagonistCharacterId, protagonistPresence, audioTarget, ambientDuckDb, holdLoopRotation).
• Deterministic 4-Phase Playback State Machine: Models entry, hold, exit, and ended phases on the player surface and backend resolver with hold-loop rotation (deterministic, shuffle, sequential) and transition exit clip rehearsing before node advancement.
• Audio Occupancy & Live Conversation Safety: Strictly validates audio manifests across character dialogue, music, and author-marked blocking effects (safeForLiveVoice is enforced false if dialogue or blocking sound effects are present). Calculates ambient ducking factors (-8 dB default) during live interaction.
• Deterministic Production Readiness Inspection: Preflight analyzers (inspectNodeProductionReadiness, inspectEpisodeProductionReadiness) inspect scenes and report actionable findings on the canvas, node editor, and validation panel without AI provider calls.

Key Changes

• server/lib/fableLoomPlayback.js & server/lib/fableLoomLimits.js: Pure helpers for audio occupancy validation, track muxing, ambient ducking math, deterministic asset resolution across phases, and production readiness analyzers.
• server/lib/fableLoomValidation.js: Zod validation schemas for audioOccupancySchema, playbackAssetsSchema, and interactionWindowSchema.
• server/services/fableLoom/records.js: Node sanitizers, patch handlers, and attachNodePlaybackAsset service helper.
• server/routes/fableLoom.js: Surface production readiness on episode validation and node readiness endpoint.
• client/src/components/fableloom/LoomPlayPanel.jsx: Rehearsal player running the 4-phase state machine, hold loop rotation, transition exit clip playback, live voice window indicator, and inspection details drawer.
• client/src/components/fableloom/LoomNodeEditor.jsx: Live interaction controls, ducking slider, hold rotation selector, and readiness findings alert.
• client/src/components/fableloom/LoomValidationPanel.jsx: Production readiness section in episode analysis.

Closes #5382