cli: `[web.wasm_opt] keep_names = true` does not keep the wasm name section in release builds

## Problem

Setting `keep_names = true` in `Dioxus.toml` `[web.wasm_opt]` has no observable effect on a 0.7.9 release web build: the shipped `.wasm` still has its name section stripped (a ~5-byte stub instead of the expected several hundred KB for a ~2 MB module). This makes function-level size attribution (twiggy & friends) and readable production stack traces impossible via the documented knob.

## Reproduction

dioxus-cli 0.7.9, `dioxus = { version = "0.7", features = ["web"] }`, Rust 1.97.

`Dioxus.toml`:

```toml
[application]
name = "web"

[web.app]
title = "…"

[web.wasm_opt]
keep_names = true
```

Two builds tried:

1. `dx build --release --debug-symbols false` + `keep_names = true` → shipped wasm 2 065 315 B, twiggy shows only unnamed `code[N]` items ("function names" subsection absent).
2. `dx build --release` (debug-symbols default true) + `keep_names = true` → shipped wasm 2 069 084 B (+3.7 KB — not a name section, which for this module is ~726 KB), still only `code[N]`, no names.

Control: the pre-bindgen `cargo build --release --target wasm32-unknown-unknown` artifact of the same workspace has a proper 726 245 B "function names" subsection, so the names exist before the dx pipeline and are removed somewhere in wasm-bindgen/wasm-opt post-processing despite `keep_names = true`.

For contrast, `WasmOptConfig.level` from the same section IS honored (verified separately), so the section itself is being read.

## Expected

`keep_names = true` produces a `.wasm` with the name section intact (docs describe it as keeping names for debugging at a size cost), or the docs/config note what else is required to make it effective.

## Environment

- dioxus / dioxus-cli 0.7.9
- binaryen version_129 (auto-installed by dx), wasm-opt completed successfully in both builds (no errors in the log)
- rustc 1.97, `wasm32-unknown-unknown`, Docker `rust:1.97-slim-trixie`, linux/arm64

Start by reproducing the two `dx build --release` cases with `keep_names = true`, then compare their shipped `.wasm` output with the pre-bindgen `cargo build --release --target wasm32-unknown-unknown` artifact. Trace the wasm-bindgen and wasm-opt post-processing described in the report, and verify completion when the shipped module retains its name section or the configuration and documentation clearly explain the required conditions.

Written by the indexing model from the issue text.