fix: luminance-aware chrome theming for light themes; serialized settings writes; buffered log flush

- Derive tab-bar/chrome palette by background luminance: light themes keep
  a near-background bar with black-tinted tab overlays instead of a muddy
  gray strip; dark themes unchanged
- Theme dockview tabs via the group-scoped --dv-*-tab-* vars its own rules
  consume (they outspecify our .dv-tab rules and leaked abyss navy onto
  light tabs); bump inactive-tab hover specificity to match
- Convert settings dialog + highlight editor hardcoded white text/border
  tints to color-mix over --chrome-fg so panes stay readable on light themes
- commands.ts: per-file log write buffer with a single drain loop per file
  (burst output coalesces into one appendFile per IO tick, chain no longer
  grows per logWrite); stop-tail rides the same buffer
- settingsStore: serialize all writers through mutateSettings() queue that
  re-reads latest state per mutation (tray close-action vs settings UI full
  saves no longer clobber each other)
- tests: burst ordering + stop-tail case for the log buffer

tests/commands-store.mjs

@@ -198,5 +198,23 @@ ok(logs.find((x) => x.file === start.file).endedAt !== undefined, 'old log final
 store.openLogsDir()
 ok(openedPath === join(userData, 'logs'), 'openLogsDir resolves to the logs dir')
 
+// ---- 6. Burst ordering + stop tail (per-file buffer + single drain) -------------
+const sid2 = 'aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee'
+const startB = store.logStart(sid2)
+// Burst 1: 300 writes in one tick must coalesce into ordered appends.
+for (let i = 0; i < 300; i++) store.logWrite(sid2, `a${String(i).padStart(3, '0')}\n`)
+await wait(10)
+// Burst 2 after a gap: may land while burst 1's drain is still in flight.
+for (let i = 0; i < 100; i++) store.logWrite(sid2, `b${String(i).padStart(3, '0')}\n`)
+// Trailing partial line must ride the same buffer via logStop.
+store.logWrite(sid2, 'partial-tail')
+store.logStop(sid2)
+await wait(200)
+const expected =
+  Array.from({ length: 300 }, (_, i) => `a${String(i).padStart(3, '0')}\n`).join('') +
+  Array.from({ length: 100 }, (_, i) => `b${String(i).padStart(3, '0')}\n`).join('') +
+  'partial-tail'
+ok(readFileSync(startB.file, 'utf8') === expected, 'burst writes + stop tail land in order')
+
 console.log('\n[commands] ALL CHECKS PASSED')
 process.exit(0)