docs(support): continue a closed chat, export one, and no transcript email

[MattDHill]

Brings the Start9 Support book in line with support-server 1.2.0 (Start9Labs/support-server#189 and #191):

• Chats: a closed chat is continued in a new linked chat, which starts from Dux's case notes, instead of being reopened. An idle close says it was due to inactivity. A new Exporting a Chat section covers the zip and its separate private folder.
• Email: only unread-reply reminders are sent; chats aren't emailed.
• Settings: the Chat transcripts switch is gone.

Merge this once support-server 1.2.0 is deployed: live-docs deploys on merge.

🤖 Generated with Claude Code

[helix-a]

One small documentation correction is needed: projects/start-docs/support/src/README.md:25 still describes the Email page as covering “Unread-reply reminders and chat transcripts, and how to turn them off.” With transcript emails and their setting removed, the guide's landing page advertises behavior that no longer exists. The proposal removes that stale phrase.

The changed pages otherwise match the merged support-server continuation and export implementations, including the single-continuation limit, carried case notes, and the top-level private/ folder covering the whole exported chain. Keep the PR's stated deployment gate before merging into live-docs.

Verification: the reviewed head merges cleanly into origin/live-docs; all applicable CI checks passed (Prettier, Conflict Markers, Docs-only), with non-doc checks skipped. On the proposal, scoped Prettier 3.8.3 and git diff --check passed, all 15 local links/anchors across the four reviewed pages resolved, and the support book built successfully through helix-build with mdBook 0.5.2 and mdbook-tabs 0.3.4. The returned HTML contains the corrected overview and linked section headings. The initial build attempt lacked mdBook; installing the documented tools resolved it.

Proposed changes: bdbd383...proposal/4204

Helix-Harness: pi
Helix-Model: openai-codex/gpt-6.1-sol