Migrate to the velocity program (Anchor 1.0)

[jordy25519]

Why

This repo was built against the old drift program (protocol-v2, Anchor 0.29, Solana 1.16). Drift was renamed/restructured into velocity (Anchor 1.0, Solana 3, program vELoC1…), so nothing here builds or targets the live program anymore. This migrates the on-chain program and the TS SDK onto velocity.

Note: the program and clients are also being absorbed into the velocity-v1 monorepo (velocity-exchange/velocity-v1#208), which is now the source of truth for the JIT clients. This PR brings the standalone repo current; once the monorepo absorption lands it can be archived.

Approach

The program depends on velocity by git rev (same pattern as the old drift dep) and the instruction interface — program id J1TnP8z…, discriminators, account layouts — is unchanged, so the vendored TS IDL stays valid. The Anchor 0.29 → 1.0 jump is the bulk of the program diff: Context collapses to a single lifetime and CpiContext::new now takes the program id (not its AccountInfo). Velocity also moved amm.min_order_size to market_stats and flattened order_tick_size onto the market.

The TS SDK becomes @velocity-exchange/jit-proxy on @velocity-exchange/sdk + Anchor 1.0, mirroring the vendored copy in the monorepo (drops the perp amm.minOrderSize dust guard velocity removed, and the removed quoteAssetAmount on the synthetic order).

Notes

• Spot JIT is removed — velocity has no spot order matching (place_and_make_spot_order is gone); spot takers return SpotOrdersNotSupported.
• The Python SDK is deleted — it depended on upstream driftpy (drift program id, PDA seeds, account layouts) and there is no velocity equivalent.
• Dropped two workflows: the python-only release.yml, and on-sdk-update.yml (auto-republished on @drift-labs/sdk updates and would collide with the monorepo publishing @velocity-exchange/jit-proxy). The verifiable-build in main.yml is bumped to velocity's toolchain image.