fix(stats): stop counting duplicate typeset subtitle lines

- Collapse animation-burst subtitle lines (karaoke OPs, animated signs) at ingest time using the same dedup rules the subtitle sidebar already applies, so repeated frames no longer flood "Top Repeated Words"
- Add retroactive cleanup for stats already affected: a "Duplicates" scanner/cleaner in the Vocabulary tab and `subminer stats cleanup --duplicate-lines` (`--dry-run`, `--lookback-days`) on the CLI
- Only subtitle lines and the vocabulary counts they feed are touched; watch time and lines-seen totals are left as recorded

src/core/services/subtitle-burst-constants.ts

@@ -0,0 +1,40 @@
+/*
+ * Thresholds that decide when a run of repeated subtitle events is one animation.
+ *
+ * Three consumers have to agree on these numbers or the same karaoke line is one cue in
+ * the sidebar and two hundred in the stats: the file-level cue dedup
+ * (`subtitle-cue-dedup`), the live gate that decides what immersion stats record
+ * (`subtitle-line-dedup-gate`), and the retroactive database cleanup
+ * (`immersion-tracker/duplicate-line-cleanup`).
+ */
+
+/**
+ * Back-to-back frames of the same animation are authored flush against each other; a
+ * tiny tolerance absorbs the centisecond rounding of the ASS timestamp format.
+ */
+export const DUPLICATE_CUE_GAP_TOLERANCE_SECONDS = 0.05;
+
+/**
+ * A burst is a *sequence*. Two adjacent events are two events, not an animation --
+ * characters do repeat each other, and a repeated line can legitimately be short.
+ */
+export const MIN_BURST_EVENTS = 3;
+
+/**
+ * Real dialogue holds on screen for about a second, so a run with a couple of much
+ * shorter events among them looks like frames. Used only alongside authoring evidence.
+ */
+export const ANIMATION_FRAME_MAX_SECONDS = 0.3;
+
+/** A karaoke run usually ends on a long "hold" frame, so not every event is short. */
+export const MIN_TAGGED_BURST_FRAMES = 2;
+
+/**
+ * SRT and VTT carry no authoring metadata at all, so timing is the only signal available
+ * -- which makes it the easiest one to get wrong. ASS->SRT conversion leaves frames at
+ * ~0.04s, well under any real utterance, and a burst leaves many of them behind. Both
+ * bounds are deliberately far stricter than the ASS path: a run of ordinary short lines
+ * (`えっ` traded between characters) must not clear them.
+ */
+export const TIMING_ONLY_FRAME_MAX_SECONDS = 0.1;
+export const MIN_TIMING_ONLY_FRAMES = 5;