Pitch

opencode parity. `/share` exports the current session as a static HTML page:

• Uploads to a configurable static-file backend (S3 / Cloudflare R2 / GitHub Gist via gh CLI).
• Returns a public URL the user can paste into Slack / GitHub / Twitter.
• Default redaction: strips API keys, env vars, file contents above N KB, anything that looks like a secret.
• Permanent option: keep until explicit `/share revoke `. Default: 7-day TTL.

Why we want this: the strongest case for any coding agent is "look at what it just did". A clickable URL beats a screenshot every time.

Implementation sketch

• New `crates/tui/src/share.rs`. Renders the session as static HTML using the same transcript renderer (existing wrapping / styling).
• Backends behind a trait so users can plug in their own.
• Default backend: GitHub gist via `gh gist create` (we already require gh CLI for the github_* tools).
• Settings: `[share] backend = "gist"`, `redact = ["api_key", "DEEPSEEK_API_KEY"]`.

Acceptance

• `/share` produces a clickable URL.
• Default redaction strips known secret patterns.
• `/share revoke ` works against the backend.
• Standard verification gates pass.