types: generate TypeScript from engine structs with tygo

tygo is pinned via go.mod's tool directive (Go 1.24+): the tool's
version is locked like any dependency and runs as 'go tool tygo', no
global install. 'go generate ./...' regenerates web/src/types/engine.ts
from Config/Result and their json tags; the generated file is committed
so the frontend builds without Go installed. The go:generate directive
anchors in a root generate.go because generate runs commands from the
declaring file's directory and tygo reads tygo.yaml from the cwd.
go.mod's ignore directive (Go 1.25+) keeps ./... from crawling into
web/node_modules, where some npm packages ship stray .go files.

tygo.yaml

@@ -0,0 +1,8 @@
+# Generates the frontend's TypeScript types from the Go structs, which are
+# the single source of truth for parameters and results (see tool-handoff.md).
+# Regenerate with: go generate ./...
+packages:
+  - path: "github.com/JustinZeus/spreadlab/internal/engine"
+    output_path: "web/src/types/engine.ts"
+    include_files:
+      - "scenario.go"