feat(previs): 预演工作台 - 重做界面与取景手势，缩放不得进入演员体积

滚轮和按钮共用最近距离，环绕目标落在演员体内时停在包围盒外；取景按可见对象体积适配入画，取消暂存手势时不写入历史。

web/src/lib/canvas/previs/previs-frame-bounds.ts

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+import { Vector3 } from "three";
+
+import { previsActorProfileForArchetype } from "@/lib/canvas/previs/previs-scene";
+import type { PrevisObject } from "@/types/previs";
+
+export type PrevisFrameBounds = {
+    min: Vector3;
+    max: Vector3;
+    span: Vector3;
+    target: Vector3;
+    fitDistance: number;
+};
+
+/** Smallest orbit distance allowed regardless of scene contents. */
+export const PREVIS_MIN_ORBIT_DISTANCE = 0.7;
+
+/** 单个对象的近似世界包围盒；演员按体积而不是原点计算，避免相机推进到身体内部。 */
+export function resolvePrevisObjectBox(object: PrevisObject): { min: Vector3; max: Vector3 } {
+    const [x, y, z] = object.transform.position;
+    const [sx, sy, sz] = object.transform.scale;
+    const actor = object.kind === "actor" || object.primitive === "character";
+    if (actor) {
+        const profile = { ...previsActorProfileForArchetype(object.archetype || "adult"), ...(object.actorProfile || {}) };
+        const actorScaleY = Math.max(0.1, Math.abs(sy) * profile.height);
+        const actorHeight = object.pose === "sit" || object.pose === "squat" ? 2.05 : profile.accessory === "horns" ? 2.8 : 2.45;
+        const halfWidth = 0.78 * Math.max(0.8, profile.shoulderWidth) * Math.max(0.1, Math.abs(sx));
+        const halfDepth = 0.72 * Math.max(0.1, Math.abs(sz));
+        return { min: new Vector3(x - halfWidth, y - 0.12 * actorScaleY, z - halfDepth), max: new Vector3(x + halfWidth, y + actorHeight * actorScaleY, z + halfDepth) };
+    }
+    const primitiveBounds: [number, number, number] = object.primitive === "sphere" ? [0.6, 0.6, 0.6] : object.primitive === "cylinder" ? [0.55, 0.8, 0.55] : object.primitive === "plane" ? [1.2, 0.05, 1.2] : [0.6, 0.6, 0.6];
+    const half = new Vector3(primitiveBounds[0] * Math.max(0.1, Math.abs(sx)), primitiveBounds[1] * Math.max(0.1, Math.abs(sy)), primitiveBounds[2] * Math.max(0.1, Math.abs(sz)));
+    return { min: new Vector3(x, y, z).sub(half), max: new Vector3(x, y, z).add(half) };
+}
+
+/**
+ * 缩放的最近距离：相机不得进入包含环绕目标的对象体积（否则背面剔除让身体消失、只剩地面阴影）。
+ * 只看包含目标的对象，大场景里推近其它区域不受整体尺寸限制。
+ */
+export function resolvePrevisZoomMinDistance(objects: PrevisObject[], target: Vector3): number {
+    let minDistance = PREVIS_MIN_ORBIT_DISTANCE;
+    const margin = 0.15;
+    objects.forEach((object) => {
+        if (!object.visible || object.primitive === "plane") return;
+        const box = resolvePrevisObjectBox(object);
+        const contains = target.x >= box.min.x - margin && target.x <= box.max.x + margin && target.y >= box.min.y - margin && target.y <= box.max.y + margin && target.z >= box.min.z - margin && target.z <= box.max.z + margin;
+        if (!contains) return;
+        // 目标到盒子最远角的距离 + 近裁剪余量，保证整个体积都在相机前方。
+        const farthest = new Vector3(Math.max(target.x - box.min.x, box.max.x - target.x), Math.max(target.y - box.min.y, box.max.y - target.y), Math.max(target.z - box.min.z, box.max.z - target.z));
+        minDistance = Math.max(minDistance, farthest.length() + 0.35);
+    });
+    return minDistance;
+}
+
+/** 可见对象（可选限定 ids）的联合包围盒，以及在给定 aspect/fov 下完整入画所需的距离。 */
+export function resolvePrevisFrameBounds(objects: PrevisObject[], ids?: Set<string>, aspect = 1, fov = 50): PrevisFrameBounds | null {
+    const visible = objects.filter((object) => object.visible && (!ids || ids.has(object.id)));
+    if (!visible.length) return null;
+
+    const min = new Vector3(Infinity, Infinity, Infinity);
+    const max = new Vector3(-Infinity, -Infinity, -Infinity);
+    visible.forEach((object) => {
+        const box = resolvePrevisObjectBox(object);
+        min.min(box.min);
+        max.max(box.max);
+    });
+
+    const target = min.clone().add(max).multiplyScalar(0.5);
+    const span = max.clone().sub(min);
+    const verticalHalfFov = (Math.max(1, fov) * Math.PI) / 360;
+    const horizontalHalfFov = Math.atan(Math.tan(verticalHalfFov) * Math.max(0.1, aspect));
+    const fitDistance = Math.max(span.y / 2 / Math.tan(verticalHalfFov), Math.max(span.x, span.z) / 2 / Math.tan(horizontalHalfFov)) * 1.08;
+    return { min, max, span, target, fitDistance };
+}