#4436 docs(harmonyos): apply the keyboard band follow-up review notes

Follow-up to #4285 (merged in 7997dc2c1). Thymikee's merge-time comment and two unresolved cubic P3 threads named four documentation-shaped notes; this applies all of them:

• snapshot help reworded to the producer's return kinds — the old sentence still said the field carries a band rect when the window table proves it smaller than the display, but the z-order-only producer can no longer publish a frame. It now states what harmonyKeyboardBandFromWindowDump returns: visibility-only per the keyboard window's z-order column, unmeasurable on a failed probe, an unreadable or conflicting z-order, or a table without the panel.
• readableZOrder moved above the z-order JSDoc so the column-comment reattaches to zOrderFromWindowRow (the helper had been dropped between the comment and its subject).
• evidence header dated — the z-order-only re-run is now attributed to 2026-11-10 at head 2878b86e4, instead of leaving the header at the 11-09 date (cubic P3).
• rect-less row test added — a panel row ending before the rect group with a readable z-order still reads visibility through its eighth token; covers the parenthetical claim in the truncated-row case (cubic P3).

Verification (this machine, worktree at 7997dc2c1):

• pnpm vitest run packages/platform-harmonyos/src/__tests__/keyboard-band.test.ts — 13 passed (1 new test)
• pnpm vitest run packages/platform-harmonyos — 20 files, 103 passed
• pnpm vitest run packages/command-surface — 39 files, 249 passed

No production behavior change; the only code motion is the helper placement.

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