## Description
Fixes#9387.
Warp already maps `.hpp` and `.hxx` files to C++ in the LSP and file
icon paths, but the syntax-highlighting language resolver only handled
`.cpp`, `.cxx`, `.cc`, `.h`, and `.hh`. This adds the missing C++ header
extensions to `language_by_filename` so `.hpp`, `.hxx`, and uppercase
`.H` files resolve to the C++ grammar for highlighting.
## Testing
- Added a regression test for `.hpp`, `.hxx`, and `.H` filename
resolution.
- `git diff --check`
- Not run: `cargo test -p languages` because this OpenClaw host does not
currently have `cargo` installed.
## Agent Mode
- [ ] Warp Agent Mode - This PR was created via Warp's AI Agent Mode
## Changelog Entries for Stable
CHANGELOG-BUG-FIX: Fixed missing syntax highlighting for C++ header
files using `.hpp`, `.hxx`, or `.H` extensions.
rkw6086
Ryan Ward