docs: document snapshot config option

[altendky]

The snapshot config field (added in 28a4517) is undocumented. It lacks both a section in the config docs page (packages/web/src/content/docs/config.mdx) and a .describe() annotation on its schema definition.

Users frequently discover the hard way that snapshots can consume enormous disk space in large repos, with no obvious way to disable them. Multiple issues reference this:

• HUGE snapshot folder #6845 — HUGE snapshot folder
• Very slow session due to 98GB of git snapshots #3182 — Very slow session due to 98GB of git snapshots
• Opencode using my 20 GB storage #10532 — Opencode using my 20 GB storage
• Snapshot feature consumes excessive disk space (170GB+ in my case) #17753 — Snapshot feature consumes excessive disk space (170GB+)
• new terminal using opencode in home dir with snapshot: true will occupy huge storage #16336 — new terminal using opencode in home dir with snapshot: true will occupy huge storage
• [FEATURE]: Snapshot lifespan ought be configurable. #10626 — Snapshot lifespan ought be configurable

A prior PR (#4753) attempted to add this documentation but was closed without merge.

What should be documented

1. A .describe() annotation on the snapshot schema field in config.ts
2. A "Snapshot" section in config.mdx explaining:
   • What snapshots do (track file changes, enable undo/revert)
   • How to disable them ("snapshot": false)
   • The tradeoff: disabling means session undo/revert becomes unavailable
   • When you might want to disable: large repos, many submodules, disk space concerns

[github-actions]

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[github-actions]

Thanks for the detailed issue! Unfortunately, it still doesn't follow one of our required issue templates.

What still needs to be fixed:

This appears to be a documentation/feature request but it doesn't use any of the three required templates. The closest match would be the Feature Request template, which requires:

• A title starting with [FEATURE]:
• The verification checkbox
• A description field

Please edit the issue to use one of the required templates:

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[altendky]

Closing to recreate using the feature request template.