FE-673: Remove obsolete side-chat highlight-to-note design doc

[kostandinang]

What

Deletes the obsolete docs/superpowers/specs/2026-05-05-side-chat-highlight-to-note-design.md.

Why

That doc was a one-shot sub-slice off the original V1.2-E sketch. It has been overtaken by the multi-chat substrate (MULTI_CHAT.md) and the FE-674 V3.0 cascade work. The canonical docs/design/SIDE_CHAT.md is still active and load-bearing — only the superseded tactical doc is going.

An earlier draft of this PR also archived SIDE_CHAT.md itself; that was wrong and has been reverted.

Test plan

• CI green

[cursor]

PR Summary

Low Risk
Low risk documentation-only change that deletes a proposed design spec; no runtime code paths are affected.

Overview
Removes the obsolete proposed design spec docs/superpowers/specs/2026-05-05-side-chat-highlight-to-note-design.md, pruning superseded side-chat highlight-to-note documentation.

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[augmentcode]

🤖 Augment PR Summary

Summary: This PR cleans up side-chat documentation by archiving older design material and removing a superseded tactical spec.

Changes:

• Moved the broad side-chat design note from docs/design/ to docs/archive/design/ to reflect that it’s no longer the live design authority.
• Deleted the obsolete “side-chat highlight-to-note” spec from docs/superpowers/specs/.

Why: Reduces clutter and prevents readers from treating superseded design notes as current guidance.

Technical Notes: This is a documentation-only change (file move + removal); no runtime behavior is affected.

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[kostandinang]

• FE-673: Remove obsolete side-chat highlight-to-note design doc #106 👈 (View in Graphite)
• main

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