docs: clarify SignPath code signing is pending, not yet implemented

[Finesssee]

What

Docs-only correction of the code-signing statements:

• README.md: the "Code signing" callout claimed Windows releases are signed for free by SignPath.io while the very next line said installers are currently unsigned. It now states signing is planned, pending onboarding — not yet wired into the release pipeline. The accurate "currently unsigned, verify the SHA-256 published alongside each release" line is unchanged.
• docs/CODE_SIGNING.md: the Build-system section described a SignPath submission step ("Release signing is submitted to SignPath from this pipeline") that does not exist in scripts/windows-release-build.ps1 or anywhere in the repo. It now opens with a Status: pending onboarding — not yet implemented note stating all current artifacts are unsigned and authenticity relies on the published SHA-256 .sha256 sidecars, labels the pipeline signing step Not yet wired, and marks the Notes section as applying once signing is active.

The signing policy, roles, and target process are kept future-ready; only the tense/placement of claims changed. No workflow code or secrets were added — no SignPath credentials exist yet.

Why

Refs #257 — during the Defender Trojan:Win32/Wacatac.B!ml investigation, both v0.47.0 artifacts verified as NotSigned and no signing step exists in the pipeline, so the docs misstated reality in both directions (README also contradicted itself in adjacent lines).

What this does NOT do

• This does not resolve, fix, or close the detection reported in Windows Defender detects CodexBar 0.47.0 installer as Trojan:Win32/Wacatac.B!ml #257. It only makes the documentation truthful. The issue stays open until the WDSI determination and/or real signed artifacts exist.
• No behavior changes; markdown only.

Checks

Docs-only change: pr-check.yml ignores docs/** and **/*.md on pull_request, so no CI jobs are expected to run for this PR.

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[Finesssee]

Independent review (posted as comment because GitHub forbids APPROVE on one's own PR): verified (1) diff touches only README.md and docs/CODE_SIGNING.md; (2) both now accurately state SignPath signing is planned/pending onboarding and that current release artifacts are unsigned with SHA-256 sidecar verification; (3) explicitly states it does NOT resolve #257 — refs only, no closing keyword; (4) markdown only, no workflow/pipeline code; (5) head MERGEABLE/CLEAN, checks skipped per pr-check.yml docs paths-ignore, zero review threads. This fixes the self-contradictory README callout and corrects the pipeline signing step description in CODE_SIGNING.md. Proceeding to merge.