fix(polyfill): include local dir deps declared in dagger-module.toml

[eunomie]

What

dagger generate on a workspace whose module declares a local directory dependency in dagger-module.toml fails:

export generated context before directory: failed to resolve dep to source:
dir module source does not contain a dagger config file

Repro: a workspace with the Go SDK and two modules where one depends on the other via a relative path (e.g. ../my-deps), then dagger generate.

Root cause

#7 added dagger-module.toml support to workspace-module-generate, but for TOML modules it returned an empty source config, on the assumption that the engine resolves includes and dependencies when the source is loaded:

if ok { // dagger-module.toml exists
    return sourceConfig{}, true, nil
}

That holds for a module's own files (loaded via "**"), but not for local directory dependencies: their directories live outside the module directory. moduleSourceInclude recurses over config.dependencies to pull each local dep's directory into the loaded context — with an empty config it never does, so the dependency's directory is dropped. The engine then loads the module as a dir source over that reduced context, resolves the dependency from its own dagger-module.toml, and fails because the dependency's directory isn't present.

Fix

Parse the dagger-module.toml dependencies (and include) so the recursion visits local dir dependencies and adds their directories to the loaded context.

• TOML decoding is isolated in parseSourceConfigTOML, with a note pointing at feat: add asTOML and TOML value type dagger#13379: once File.asTOML ships and the helper's dagger.io/dagger is bumped, the local decode can be replaced by reading the fields through the engine API (dropping the pelletier/go-toml dependency).
• Adds github.com/pelletier/go-toml v1.9.5 (same lib/version the engine uses).

Tests

• TestParseSourceConfigTOMLReadsDependenciesAndInclude — TOML deps/include parse correctly.
• TestModuleSourceIncludeReadsTOMLDependencies — a module whose dependency is declared only in dagger-module.toml now includes the dependency's directory.

go build, go vet, gofmt, go test all clean.

A polyfill-e2e end-to-end .generate check (with a dagger-module.toml fixture) is a sensible follow-up but needs a CLI-1.0 dev engine to validate; left out of this PR.