build: include .sqlx/ in cala-ledger package for Nix vendoring

[nicolasburtey]

Summary

• Add explicit include directive to cala-ledger's Cargo.toml so the .sqlx/ offline query cache is included when vendoring the crate
• Needed for SQLX_OFFLINE=true builds in Nix

Test plan

• SQLX_OFFLINE=true cargo check -p cala-ledger succeeds
• Nix build succeeds with vendored dependencies

🤖 Generated with Claude Code

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Note

Low Risk
Packaging-only change that affects what files are included in the crate tarball; runtime behavior is unchanged, with minimal risk aside from slightly larger published artifacts.

Overview
Updates cala-ledger/Cargo.toml to add an explicit package.include list so the crate publish/vendor contents include .sqlx/** (along with src/, migrations, schemas, tests, etc.), enabling offline sqlx builds when dependencies are vendored (e.g., Nix with SQLX_OFFLINE=true).

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