docs(packaging): per-package READMEs + English descriptions for NuGet (…

…#36)

The published 1.0.0 packages showed no README and a Spanish <Description>
(a residue of the English migration that lived in the .csproj, not a
comment). Fix both in the package metadata so the next release (1.0.1)
ships correct, embedded content.

- Directory.Build.props: PackageReadmeFile=README.md + pack each publishable
  library's own README.md into its .nupkg.
- Six per-package README.md (Core, Versioning, Server, Loro,
  Persistence.EFCore, Persistence.Redis): what it provides, install, a short
  snippet, links (absolute URLs so they resolve on nuget.org).
- Translated the six <Description> values to English.

Verified: dotnet pack embeds README.md (<readme> in the .nuspec) and the
English description; markdownlint clean; build green. 1.0.0 packages are
immutable, so this lands in 1.0.1.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fix(release): SC-009 gate uses dumpbin on Windows (strings was blind) (…

…#35)

The release dry-run failed only on native (win-x64): the SC-009 gate
("test hooks NOT exported") lists symbols with `strings` for .dll files,
but `strings` cannot reliably read a PE export table — it missed even the
`abi_version` positive control, so the gate correctly refused a verdict
("blind, not clean") and failed. The other three RIDs (nm) pass; the code
and the binaries are fine — only the Windows inspection method was wrong.

Switch the .dll path to `dumpbin -exports` (the canonical tool for a PE
export table), made available via ilammy/msvc-dev-cmd on the Windows runner.
The positive-control + both-hooks logic is unchanged.

Latent gate (not introduced recently); surfaced by the pre-publish dry-run.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>