Add Codex ingestion provider and Windows Chroma launch fix

[flipjam]

Summary

• add Codex as a first-class ingestion provider with settings/defaults, route dispatch, and worker health reporting
• fail closed when Codex is selected but the Codex executable is unavailable instead of falling back to another provider
• launch chroma-mcp on Windows via direct uvx.exe resolution instead of cmd.exe /c uvx

Local verification

• npm run build
• /api/health reports provider codex on the local worker
• /api/chroma/status?deep=true returns healthy with semantic round-trip success
• pending queue drains after Codex ingestion

Notes

This is a draft PR opened from a local durability fix. It intentionally contains source-level changes only; generated marketplace bundle files are not included in this branch.

[thedotmack]

Closing this draft: the Windows Chroma launch half landed via #2847 (direct uvx spawn), and the Codex ingestion provider half overlaps the open provider work (#2514/#2764, plan-12 #2785). Re-cut the ingestion piece against current main if still wanted.