Add 1.5.0 release notes

[hhvrc]

Summary

• Consolidated release notes for 1.5.0 from all RC entries (rc.1 through rc.6)
• RC entries left untouched

Review

Please review the release notes for accuracy and completeness before merging to beta.

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[changeset-bot]

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Latest commit: 27b9651

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[Copilot]

Pull request overview

Adds consolidated Version 1.5.0 release notes at the top of CHANGELOG.md, summarizing the user-visible changes that were previously spread across 1.5.0-rc.1 through rc.6, while leaving the RC entries unchanged.

Changes:

• Introduced a new # Version 1.5.0 Release Notes section summarizing highlights and major areas (Radio/Timing, Captive Portal, E-Stop, System, HTTP/Gateway).
• Documented breaking changes and notes relevant to upgrades (re-pairing Petrainer shockers, AssignLCG endpoint change, CRLF serial output).
• Added a consolidated bug-fix and internal-changes summary for 1.5.0.

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[Copilot]

This repeats the RFC reference; if you update earlier to "RFC 8908", update this line as well so the changelog uses a consistent RFC citation format.

[Copilot]

"RFC-8908" isn’t the standard way RFCs are referenced in text; RFCs are typically cited as "RFC 8908". Consider updating the wording here (and any repeated mentions below) for correctness and consistency.