fix get_state referenceerror, restore extractVideoId import, log failing handlers
GET_STATE still called getWatchedIds(), which 0.3.0 deleted when the watched
store became a { videoId: watchedAtMs } map — five of six call sites were
renamed to getWatched(), this one was missed. Every settings read goes
through GET_STATE, so the popup, the settings page, and the content-script
cache all silently fell back to their built-in defaults on load while
SET_SETTINGS kept writing to storage correctly: preferences looked like they
never saved.

youtube-feed.js used extractVideoId without destructuring it from YTWash, so
the IntersectionObserver callback threw on every sighting and the Repeat
Video Fixer never recorded a count.

Rejected message handlers now log the failing message type — both bugs were
invisible because a throwing handler only ever surfaces as a UI that quietly
stops updating.

See all commit history at the public Github page posted here: https://github.com/k0shir0/feedcleaner

Add Repeat Video Fixer; flip placeholder default; apply review fixes
Counts feed-card viewport sightings (>=50% visible, once per video per
SPA navigation) via IntersectionObserver, batched to the background and
stored in storage.local.seenCounts with last-seen pruning. Cards seen at
least repeatThreshold times before (default 1, configurable 1-10) are
hidden with the same hard-hide/placeholder modes as the Watch Filter;
repeat placeholders offer a "Show anyway" per-video count reset.

Hide decisions use sighting counts snapshotted at navigation time so a
card never disappears while it is being looked at; the snapshot only
syncs downward mid-page (resets/clears).

placeholderMode now defaults to true for new installs.