feat(canvas): 新增视频节点字幕体系与多轨时间线编辑（关联 #187） (#191)

* fix(ci): 后端测试 - 修复 responses 流式测试数据与 Grok 生图测试 SSRF 放行

* feat(canvas): 新增视频节点字幕体系与多轨时间线编辑（关联 #187）

---------

Co-authored-by: zhaoyue <zhaoyue@rongshantech.com>

web/src/lib/timeline/subtitle-highlights.ts

@@ -0,0 +1,91 @@
+import type { SrtEntry, SubtitleHighlight } from "@/types/timeline";
+
+export function isValidSubtitleHighlight(entry: SrtEntry | undefined, highlight: SubtitleHighlight): boolean {
+    if (!entry || entry.index !== highlight.entryIndex) {
+        return false;
+    }
+
+    if (highlight.start < 0 || highlight.end <= highlight.start) {
+        return false;
+    }
+
+    if (highlight.end > highlight.sourceText.length) {
+        return false;
+    }
+
+    return highlight.highlightText === highlight.sourceText.slice(highlight.start, highlight.end);
+}
+
+export function isExpiredSubtitleHighlight(entry: SrtEntry | undefined, highlight: SubtitleHighlight): boolean {
+    if (!entry || entry.index !== highlight.entryIndex) {
+        return true;
+    }
+
+    return entry.text !== highlight.sourceText;
+}
+
+export function filterValidSubtitleHighlights(entries: SrtEntry[], highlights: SubtitleHighlight[]): SubtitleHighlight[] {
+    const entryMap = new Map(entries.map((entry) => [entry.index, entry]));
+
+    return highlights.filter((highlight) => {
+        const entry = entryMap.get(highlight.entryIndex);
+        return isValidSubtitleHighlight(entry, highlight) && !isExpiredSubtitleHighlight(entry, highlight);
+    });
+}
+
+/**
+ * 在重分段后，把旧高亮映射到新条目上。
+ * 规则：highlightText 必须作为子串出现在某个新条目的 text 中；
+ * 找到第一个匹配的条目，更新 entryIndex 和 start/end；
+ * 找不到则放入 dropped（通常是跨切分点的关键词）。
+ */
+export function remapHighlightsAfterResegment(oldHighlights: SubtitleHighlight[], newEntries: SrtEntry[]): { remapped: SubtitleHighlight[]; dropped: SubtitleHighlight[] } {
+    const remapped: SubtitleHighlight[] = [];
+    const dropped: SubtitleHighlight[] = [];
+
+    for (const highlight of oldHighlights) {
+        const target = newEntries.find((entry) => entry.text.includes(highlight.highlightText));
+        if (!target) {
+            dropped.push(highlight);
+            continue;
+        }
+        const start = target.text.indexOf(highlight.highlightText);
+        remapped.push({
+            entryIndex: target.index,
+            start,
+            end: start + highlight.highlightText.length,
+            highlightText: highlight.highlightText,
+            sourceText: target.text,
+        });
+    }
+
+    return { remapped, dropped };
+}
+
+// 无可用大模型配置时的本地回退：按终止标点取首段作为高亮，保证功能不中断。
+const TERMINAL_PUNCTUATION = "。！？；";
+
+export function buildFallbackHighlights(entries: SrtEntry[]): SubtitleHighlight[] {
+    const highlights: SubtitleHighlight[] = [];
+    for (const entry of entries) {
+        let terminalIndex = -1;
+        for (let i = 0; i < entry.text.length; i += 1) {
+            if (TERMINAL_PUNCTUATION.includes(entry.text[i])) {
+                terminalIndex = i;
+                break;
+            }
+        }
+        if (terminalIndex <= 0) {
+            continue;
+        }
+        const end = terminalIndex + 1;
+        highlights.push({
+            entryIndex: entry.index,
+            start: 0,
+            end,
+            highlightText: entry.text.slice(0, end),
+            sourceText: entry.text,
+        });
+    }
+    return highlights;
+}