Remove stale net6.0 references

[mtmk]

net6.0 was already dropped from the target frameworks (now netstandard2.0, netstandard2.1, net8.0, net10.0). This removes leftover net6.0 mentions from the platform-compatibility docs and corrects csproj and script comments that still labelled netstandard-only dependency groups as net6.0.

Part of #948.

[synadia-claude-reviewer]

Claude finished @mtmk's task in 1m 39s —— View job

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PR Review: Remove stale net6.0 references

• Gather PR diff and context
• Review changed files
• Post review findings

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This is a straightforward documentation and comment cleanup — no logic changes. All four files are consistent with the actual target frameworks in src/Directory.Build.props (netstandard2.0;netstandard2.1;net8.0;net10.0).

Findings:

scripts/apicompat.sh — Minor wording ambiguity in the new comment: it reads "Compare the netstandard surfaces against net8.0 as the baseline TFM", but in check_compat, the first argument is named baseline_tfm and is occupied by netstandard2.0/netstandard2.1 — meaning netstandard is the baseline and net8.0 is the target. "…against net8.0 as the target TFM" would be more precise. Not a functional issue.

Separately, apicompat.sh now checks netstandard2.0 and netstandard2.1 against net8.0, but not against net10.0, which is now a first-class TFM. If API surfaces diverge between net8.0 and net10.0, that gap would go undetected. This is arguably out of scope for this cleanup PR, but worth a follow-up.

NATS.Client.JetStream.csproj — New comment is accurate. The IsTargetFrameworkCompatible condition correctly targets netstandard-only builds.

NATS.Client.Serializers.Json.csproj — New comment is accurate. The explicit string equality condition works correctly for the current TFM set. Note this uses explicit == 'netstandard2.0' OR == 'netstandard2.1' while JetStream.csproj uses the more robust IsTargetFrameworkCompatible — but this inconsistency predates the PR.

platform-compatibility.md — All substitutions are correct: net6.0 → net10.0 in the TFM list, the TLS table, and both AddNats signature headings.

Summary: No bugs, no security issues. The two minor points (comment wording in apicompat.sh, missing net10.0 compat check) are low-priority and can be addressed separately. The PR is good to merge as-is.

[scottf]

LGTM