WASM: complete Windows-host support for @columnar-tech/dbc-wasm

[zeroshade]

Tracks finishing Windows-host support for the @columnar-tech/dbc-wasm package (introduced in #395). Linux and macOS are validated in CI; Windows is experimental and dropped from the WASM CI matrix until the issue below is resolved.

Fixed on the way (already on the branch / in #395)

• Env-size overflow: boot.cjs no longer forwards the full process.env into the wasm runtime. A GitHub Actions Windows env is large enough to overflow wasm_exec.js's combined argv+env size cap, making go.run() throw before startup. Now only the vars GOOS=js needs are forwarded (HOME/XDG_*/TMPDIR), via curateGoEnv().
• Temp dir: GOOS=js os.TempDir() reads only $TMPDIR (else /tmp, missing on Windows). curateGoEnv() maps TMPDIR from %TMPDIR%||%TEMP%||%TMP% and normalizes backslashes.

With those, the Windows runtime boots and install() completes.

Remaining blocker

listInstalled() returns [] on Windows even though install() wrote the manifest. Repro (from the WASM windows-latest smoke):

• installDir contains test-driver-1.toml at the top level (confirmed via Node fs.readdirSync).
• dbc.listInstalled(installDir) → config.FindDriverConfigsIn(\"C:/.../installDir\") → loadDir → returns no drivers.

Switching loadDir from fs.Glob(os.DirFS(dir), \"*.toml\") to os.ReadDir(dir) did not help (identical empty result), so it's not the os.DirFS abstraction. Leading hypothesis: under GOOS=js, a normalized drive-letter path like C:/Users/... is not treated as absolute (filepath.IsAbs is false on the unix-like js target), so the runtime's path resolution for discovery diverges from where install actually wrote. Needs Go-side, syscall-level diagnostics on a real Windows runner (os.Stat/ReadDir/Open results + the exact resolved path inside loadDir).

Action

• Re-add windows-latest to .github/workflows/wasm.yml once discovery works.
• Pin down the GOOS=js + Windows drive-path resolution behavior in config driver discovery.
• Decide whether the loader should canonicalize Windows locations to a wasm-fs-absolute form before handing them to Go.