refactor(vision): fold Vision settings into the Compaction sidebar view

Both pertain to compaction (message compaction + image compaction), so they
share one sidebar panel. Removes the standalone "Vision" view kind; the
VisionSettingsView now renders inside the Compaction panel, below
CompactionView (with an "Image compaction" divider).

CompactionView stays keyed per conversation (its percent is per-conversation);
VisionSettingsView stays un-keyed (its settings are global). The vision
feature library + manifest are unchanged (still a composed module).

A persisted "vision" sidebar panel gracefully renders empty (the kind is no
longer in viewKinds) until the user re-selects Compaction.

Verification: svelte-check 0/0; vitest 959/959; biome clean; build OK.

Not merged or pushed.

0 files changed, 0 insertions, 0 deletions