[#446 Tier 1 #5 follow-up] examples/wasm-exports-demo.affine — end-to-end usage demo #500

Context

Closed #455 shipped via PR #467 (Deno-ESM wasm_export_call + WasmValue + JS codegen). The smoke-test landed inline (tests/codegen-deno/wasm_call.{affine,harness.mjs} exercises the prior wasmCall surface and gets supplemented by the new export-call dispatch under the same harness).

A stand-alone usage demo under examples/ was deferred per the owner scope breakdown:

Example: examples/wasm-exports-demo.affine loading a tiny wasm + invoking an export end-to-end

This issue tracks that.

Scope

A copy-paste-ready, well-commented example in examples/ that:

1. Reads a tiny .wasm module from disk (or embeds it via a base64 constant).
2. Instantiates it via existing stdlib/Deno.affine wasmInstance (or WebAssembly.instantiate host bridge).
3. Builds a [WasmValue] argument list using the new constructors (wv_i32 / wv_i64 / wv_f32 / wv_f64).
4. Calls wasm_export_call(exports, "fn_name", args) and uses wv_as_int / wv_as_float / wv_kind to decode the result.
5. Demonstrates each of the four WasmValue kinds via a multi-export module (e.g. addI32, addI64, mulF32, mulF64).

Acceptance

• examples/wasm-exports-demo.affine lands with SPDX header + extensive top-of-file docstring.
• Compiles via --deno-esm end-to-end.
• Runs as a smoke-test (either added to tools/run_codegen_deno_tests.sh or as a stand-alone just demo-wasm-exports recipe).
• Round-trips one of each WasmValue kind successfully.
• Referenced from the bindings-roadmap.adoc Tier 1 ci: Bump actions/github-script from 7.0.1 to 8.0.0 #5 row (or its surrounding "Worked example" note) as the canonical end-to-end demo.

Refs

• Closed kickoff: [#446 Tier 1 #5] WASM-exports calling pattern (recommended kickoff) #455
• Shipped surface: PR feat(stdlib): WasmValue + wasm_export_call typed wasm-exports binding (closes #455) #467 — stdlib/Deno.affine WasmValue + wasm_export_call
• Existing harness: tests/codegen-deno/wasm_call.{affine,harness.mjs} (round-trips the prior wasmCall surface via a hand-built 41-byte add(i32, i32) -> i32 module)
• Umbrella: [campaign] AffineScript top-50 framework bindings roadmap (UMBRELLA) #446 (Tier 1 — idaptik blockers)
• Tier sub-issue: [#446 STEP 2] Tier 1 — idaptik blockers (10 bindings) #450
• Doc to cross-reference from: docs/bindings-roadmap.adoc Tier 1 row ci: Bump actions/github-script from 7.0.1 to 8.0.0 #5