Simplify release workflow and isolate Iseberg validation

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• Remove the PowerShell-version matrix from the main release workflow and run terminal-only managed tests once per operating system.
• Move extended Iseberg App/UI/Settings/Settings.Editor coverage to a separate workflow with pinned PowerShell 7.6.6 on Windows/Linux/macOS. Trigger it on source/dependency changes, weekly, and manually; cancel superseded runs.
• Move terminal-only Windows x64/ARM64 NativeAOT publish checks to the separate workflow.
• Run Linux/macOS packaging and Control NuGet packing alongside platform tests; keep final release publication gated on the existing main-workflow platform tests, native runtime checks, and package/signature validation.
• Skip Linux reproducibility rebuilds for tag/manual releases while retaining them in ordinary CI.
• Update release and Iseberg documentation.

Upstream integration

Rebased onto master commit bda58de, which makes Iseberg NativeAOT-safe and enables it in release payloads. Preserve those upstream defaults, the private PowerShell module payload, and mandatory module signature verification. Extended engine/workbench coverage runs independently rather than gating release publication; release artifacts continue to include Iseberg.

Motivation

Release run 37976537406 spent about 70 minutes in a Windows build/test job, including 62 minutes in the Iseberg-enabled UI suite. Linux/macOS packaging also waited for managed test jobs despite not consuming their outputs.

Validation

• Actions lint passed for both rebased workflows.
• Dependency/configuration assertions confirmed matrix removal, parallel packaging, retained final release gates, and preservation of upstream Iseberg release payload/signature behavior.
• No conflict markers or whitespace errors remain.
• Before rebase, full Windows terminal-only suite: 2,035 passed, 0 failed, 11 skipped. This result is from the previous base, not the new master commit.
• Actual Linux/macOS execution, the changed upstream production code, and hosted-run elapsed-time improvement remain CI validation.