chore: [CLD-2844] deprecate sfcompute/cli

[0xJepsen]

What

Deprecate the legacy TypeScript sf CLI ahead of archiving this repo.

Part of the CLD-2844 plan (from this Slack thread):

• Update README
• Add a deprecation warning to the CLI on startup
• Release new release
• Archive the repo (done manually after this merges — archiving makes the repo read-only, so it has to come last)

Changes

• src/lib/migrate.ts — the startup migrate banner is now a red "Deprecated" notice: "This CLI is deprecated and no longer maintained." It keeps the sf migrate call-to-action, the docs link, and the SF_CLI_DISABLE_MIGRATE_BANNER opt-out. No change to when it shows (still skipped for --json, migrate/upgrade, opted-out, and already-migrated users).
• README.md — leads with a > [!WARNING] deprecation block pointing at the Rust CLI (install + migration guide). Existing docs kept below for archival reference.

Banner preview

╭───────────────────── Deprecated ─────────────────────╮
│                                                      │
│   This CLI is deprecated and no longer maintained.   │
│                                                      │
│   The sf CLI has been rewritten in Rust. Run         │
│   'sf migrate' to switch. Your current CLI           │
│   stays available as 'sf-old'.                       │
│                                                      │
│   Docs:  https://sfcompute.com/migrate               │
│   Hide:  SF_CLI_DISABLE_MIGRATE_BANNER=1             │
│                                                      │
╰──────────────────────────────────────────────────────╯

Verification

• tsc --noEmit passes clean.
• biome check reports only pre-existing warnings in untouched src/lib/scale/ files.

Notes

• The banner change only reaches installed users once a new version is published — flag if we want a release cut, otherwise landing the code + archiving is enough.

🤖 Generated with Claude Code

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
src/lib/migrate.ts	17% smaller
README.md	Unsupported file format

[sigmachirality]

we need to release a new release after this merges, but otherwise lgtm