v0.5.2

Fixes two ways the built-in full-text index could stall, both seen on a production vault after upgrading to 0.5.1:

• A pass that found pending notes but indexed none of them (all skipped) left its phase marker unsettled, so the next pass counted it as an interrupted attempt; after three such passes the index disarmed itself with "full-text pass was interrupted 3 times". Such a pass now writes a segment-empty marker.
• A note whose recorded hash (index_state.hash) never matched its current body was skipped as "moved on" on every pass and stayed pending forever, re-arming a pass on every request. It is now indexed as its body is, under the recorded hash; a body that really did change has its change in the feed, which re-queues the note.

The index version meta is bumped to 5, so a vault disarmed this way recovers on its first start after upgrading.