generate: stage local dependency closure before codegen

[tiborvass]

Uses the new ModuleSource.generateLocalDependencies engine API. Before generating each managed PHP module, generateAll (the @generate function) and Mod.generate stage the transitive local dependency closure onto the workspace via withChanges, then generate against the staged workspace. This lets PHP module codegen see up-to-date dependency bindings, including dependencies owned by other SDKs.

The existing github.com/dagger/polyfill@main dependency is advanced to the module-generation scoping fix, so each generated changeset contains files for only that module.

Depends on

• feat: ModuleSource.generateLocalDependencies dagger#13715 — ModuleSource.generateLocalDependencies ✅ merged
• fix: scope module generation to the module path polyfill#5 — scope module generation to the module path ✅ merged

This is the PHP SDK equivalent of dagger/typescript-sdk#12 and dagger/go-sdk#12.

Validation

• jq empty dagger.json
• (cd helpers/render-template && go test ./...)
• git diff --check

A full generation test was not run locally because the installed stable CLI (v0.21.7) predates the CLI-1.0 engine API used here.