docs: publish clear, user-purpose-first Scient Help

[yaacovcorcos]

Summary

• publish the final 31-page Desktop Help corpus with concise, practical guidance for humans and agents
• explain projects, Sources, provider setup, Message Scient, voice, files, scientific workflows, recovery, and permission boundaries from the user perspective
• fold conversation forking and provider switching into Message Scient
• move unreleased mobile behavior to an explicit internal release hold
• preserve relevant technical instructions while removing obsolete migration and implementation detail

Consolidation

This is the durable net result of documentation PRs #195, #196, #197, and #198 plus the final user-purpose review. Those temporary qualification and retirement layers remain available as review history but do not need to churn through main.

Verification

• 31 public Help Markdown pages
• local links checked across 33 files
• 6 Markdown link-checker tests passed
• staged formatting hook passed
• git diff check passed
• direct installer endpoints verified against the public Scient release service

Documentation impact

This PR is the documentation outcome. It changes public Help and one internal release-hold record; it does not change product runtime behavior.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.3 KiB	13.3 KiB	+19 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+1 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+18 B (+0.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.6 KiB	55.6 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.3 KiB	+37 B (+0.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−7 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+44 B (+0.7%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.4 KiB	56.4 KiB	+44 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	9	10	+1 (+11.1%)	21	✅

Baseline: c69278e · PR result: 5a84cc9 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 109.5 KiB
• Claude decoded thread snapshot: 110.2 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.