fix(dashboard): read cached EPG timestamps as unix seconds (#1532)

`epgTimestampMs` in the dashboard live-EPG helpers returned
`EpgProgram.startTimestamp`/`stopTimestamp` as-is, but those fields are
unix SECONDS everywhere else (`getProgramTimeMs` in `@iptvnator/ui/epg`
multiplies by 1000). The bug was latent: the backend
`GET_CURRENT_PROGRAMS_BATCH` rows never set the fields, so the ISO
fallback always ran.

Scale a positive finite timestamp by 1000 and treat zero/non-finite
values as absent, mirroring `getProgramTimeMs`. Add a dedicated spec
that feeds seconds-based timestamps and asserts the formatted range and
progress, and fix the rails component spec fixture, which stored
millisecond values in the seconds fields and so encoded the old bug.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

.changes/dashboard-live-epg-timestamp-units.md

@@ -0,0 +1,9 @@
+---
+type: internal
+area: dashboard
+---
+
+The dashboard's live "now playing" time range and progress bar now read
+pre-computed EPG timestamps as unix seconds, matching the rest of the EPG
+code. Today's dashboard lookups never carry those fields, so nothing changes
+on screen; this closes the gap before a future data path supplies them.