Add LQL function bodies and current setting builtin

[MelbourneDeveloper]

Summary

• add bodyLql support for PostgreSQL functions, including YAML validation, DDL generation, and diff idempotence
• add PostgreSQL current_setting('key') support in LQL policy predicates and function bodies
• add broad NAP-shaped tests covering session keys, casts, helper functions, exists pipelines, and real Postgres RLS behavior

Validation

• dotnet csharpier check .
• make lint
• dotnet test Lql/Nimblesite.Lql.Tests --configuration Release --verbosity minimal
• dotnet test Migration/Nimblesite.DataProvider.Migration.Tests/Nimblesite.DataProvider.Migration.Tests.csproj --configuration Release --no-build --verbosity minimal
• dotnet test Migration/Nimblesite.DataProvider.Migration.Tests/Nimblesite.DataProvider.Migration.Tests.csproj --filter "FullyQualifiedName~RlsCurrentSettingLqlTests|FullyQualifiedName~PostgresFunctionBodyLqlTests|FullyQualifiedName~PostgresFunctionBodyLqlE2ETests" --configuration Release --verbosity minimal
• dotnet test Sync/Nimblesite.Sync.Tests --configuration Release --no-build --verbosity minimal
• dotnet test Sync/Nimblesite.Sync.SQLite.Tests --configuration Release --no-build --verbosity minimal
• dotnet test Sync/Nimblesite.Sync.Postgres.Tests --configuration Release --no-build --verbosity minimal
• dotnet test Sync/Nimblesite.Sync.Integration.Tests --configuration Release --no-build --verbosity minimal
• dotnet test Sync/Nimblesite.Sync.Http.Tests --configuration Release --no-build --verbosity minimal
• dotnet test Reporting/Nimblesite.Reporting.Tests --configuration Release --no-build --verbosity minimal
• dotnet test Lql/Nimblesite.Lql.TypeProvider.FSharp.Tests --configuration Release --no-build --verbosity minimal

Notes

• make test was not used for the final pass because the Nimblesite.DataProvider.Example.Tests make target hung in nested build startup locally; the same test project passed when rerun directly with --no-build earlier in this branch.
• Reporting.Integration.Tests initially needed the local Playwright Chromium install; after install, the run hit existing .report-* DOM timeouts unrelated to the LQL/Migration changes and was stopped.