fix(compiler): support goscript deploy embed fs

[paralin]

• preserve GoScript CLI/package build flags through compiler package graph loading

• add embed.FS compiler/runtime support needed by Bldr deploy bundles

• keep generated deploy assets addressable for the Spacewave GoScript compiler mode

• go test ./compiler ./cmd/goscript -run "TestCompilePackagesUsesEmbedOverride|TestCompilePackagesEmbedsFS|TestCompileCommand.*BuildFlags|TestPackageGraphHonorsBuildFlags"

• bun test gs/embed/index.test.ts

• git diff --check

[Copilot]

Pull request overview

Enables real embed.FS support end-to-end so the GoScript compiler/runtime can lower //go:embed declarations targeting embed.FS (including directory and glob patterns) and serve the embedded files through the standard io/fs APIs at runtime. Also tidies a build-flag helper.

Changes:

• Add compiler lowering for embed.FS (directory walks, globs, all: prefix) emitting a markAsStructValue(new embed.FS(new Map(...))) literal, with helper refactors for pattern cleaning and file reads.
• Rewrite the gs/embed runtime override to back FS with a file map and implement Open, Read, ReadDir, Stat, Close, and clone(), including supporting embedFile, embedFileInfo, embedDirEntry types and a ValidPath-based validatePath helper.
• Replace a manual loop with slices.Contains in compiler/build-flags.go and add Go+Vitest tests for the new behaviors.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
compiler/build-flags.go	Minor refactor to use slices.Contains when checking for an existing build tag.
compiler/lowering.go	Adds embed.FS lowering plus directory/glob expansion and refactors go:embed pattern/read helpers.
compiler/skeleton_test.go	New TestCompilePackagesEmbedsFS exercising direct, directory, and glob go:embed patterns into embed.FS.
gs/embed/index.ts	Implements a functional embed.FS runtime with Open/Read/ReadDir/Stat/Close and clone() plus supporting internal classes/helpers.
gs/embed/index.test.ts	Vitest coverage for cloning, io/fs.ReadFile/ReadDir/Stat, and direct Open/Read/ReadDir iteration.

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