Fix stats command flow and tracking metrics regressions

- Route default `subminer stats` through attached `--stats`; keep daemon path for `--background`/`--stop`
- Update overview metrics: lookup rate uses lifetime Yomitan lookups per 100 tokens; new words dedupe by headword
- Suppress repeated macOS `Overlay loading...` OSD during fullscreen tracker flaps and improve session-detail chart scaling
- Add/adjust launcher, tracker query, stats server, IPC, overlay, and stats UI regression tests; add changelog fragments

stats/src/lib/media-session-list.test.tsx

@@ -23,6 +23,8 @@ test('MediaSessionList renders expandable session rows with delete affordance',
           lookupCount: 3,
           lookupHits: 2,
           yomitanLookupCount: 1,
+          knownWordsSeen: 6,
+          knownWordRate: 25,
         },
       ]}
       onDeleteSession={() => {}}