docs: sweep sync follow-ups into their owning version docs

Kaizen/postmortem next-steps kept accumulating with no owner. Each item
now lives in one version doc (v0.7 sync perf, v0.9 robustness, v1.0
boot) with the source docs linking there; the editor-freeze safety net
is marked hardware-verified and the v0.5 walk re-measure closed at 4.3s.

docs/v1.0-polish.md

@@ -5,8 +5,12 @@
 
 **Status:** not started.
 
-- [ ] Boot time ≤ 3 s to usable cursor — currently ~4.26 s; the ~1.9 s cold-boot
-      full refresh is a hard e-ink floor, so ≤ 3 s is marginal (see
+- [ ] Boot time ≤ 3 s to usable cursor — 4.26 s at v0.1 ship; **regressed to
+      ~8.7 s on a real 1098-file card** once the v0.5 palette walk joined the
+      boot path (4.3 s of readdir-over-SPI, already d_type-optimised — see the
+      [v0.5 walk amendment](v0.5-palette-and-multi-file.md)), so the walk must
+      go async/deferred, and the ~1.9 s cold-boot full refresh + ~0.74 s PSRAM
+      memtest are the remaining levers (see
       [`notes/boot-time-budget.md`](notes/boot-time-budget.md))
 - [ ] Font selection (at least one serif + one mono) with adjustable font
       size, switchable at runtime and persisted across reboots