chore: release v0.7.0

[joshuajbouw]

Release the SDK at 0.7.0 to align with unicity-astrid/astrid 0.7.0 (per-domain WIT host ABI). Workspace was bumped 0.6.1 → 0.7.0 as part of #44; this issue tracks the release-bundle roll-up + publish.

Checklist:

• Cargo.toml workspace version at 0.7.0 (already bumped in feat(sdk)!: migrate to per-domain WIT + wasm32-unknown-unknown #44)
• CHANGELOG.md [Unreleased] rolled into [0.7.0] with date
• cargo test --workspace passes
• cargo clippy --workspace -- -D warnings clean
• Tag v0.7.0 after merge
• cargo workspaces publish --from-git (publishes astrid-sys, astrid-sdk-macros, astrid-sdk in dep order)

Pairs with the merged unicity-astrid/astrid v0.7.0 release. Capsules pin astrid-sdk = "0.7" once this publishes.