docs: update changelog for v0.29.0

[augmentmoogi]

Update the changelog with the v0.29.0 release notes.

• Document new capabilities including prompt modules, expanded cloud session management commands, the built-in auggie-guide subagent, and daemon support for plain Spaces and child-agent indexing.
• Summarize product and developer experience improvements across session metadata, daemon indexing visibility, MCP reliability, the CLI welcome screen, and str-replace-editor compatibility.
• Capture bug fixes for Windows upgrades, MCP header handling, daemon auth-session recovery, markdown fence carryover, paginated message ordering, and subagent delegate rendering.

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[augmentmoogi]

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