Bundled Boost 1.86.0 fails to compile under recent Clang - `template` keyword misuse in `boost::qvm`, fixed upstream in 1.87.0+

## Summary

`cmake/boost.cmake` pins Boost to 1.86.0. That version's bundled `qvm` library (used by this plugin's own room/speaker-geometry code, via `common/components/src/room_views/Coordinates.h`) fails to compile under a sufficiently recent Clang:

```
build/_deps/boost-src/libs/qvm/include/boost/qvm/quat_traits.hpp:82:30: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
quat_traits::template write_element_idx(i, q) = s;
^
build/_deps/boost-src/libs/qvm/include/boost/qvm/quat_traits.hpp:92:30: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
quat_traits::template write_element_idx(i, q, s);
^
```

I hit this independently a while back (documented [here](https://gist.github.com/mormegil6/65f94cd804b924531ec9ac135cd2b09b), alongside the unrelated #10 and #20 workarounds needed at the time) and worked around it by hand-patching the fetched source post-configure:

```
sed -i '' '82s/template //;92s/template //' build/_deps/boost-src/libs/qvm/include/boost/qvm/quat_traits.hpp
```

That works, but it's a manual step that has to be redone on every clean `build/` directory. There's a real fix available instead.

## Root cause

This is [boostorg/qvm#54](https://github.com/boostorg/qvm/issues/54) - `template` used as a disambiguator before a name that isn't followed by an explicit template argument list, which newer Clang correctly rejects per the standard (see the linked [LLVM discussion](https://github.com/llvm/llvm-project/issues/101079)). It's not an Eclipsa bug and not a JUCE bug - purely upstream Boost, in a header this plugin's own code pulls in transitively through `boost/qvm.hpp`.

It was fixed upstream in [boostorg/qvm@c4b9c063a0](https://github.com/boostorg/qvm/commit/c4b9c063a0) ("Fix for issue 54") - the fix is exactly the same one-line-per-site change as the manual patch above, just applied at the source. Boost 1.86.0's bundled `qvm` submodule commit predates that fix by about a month; **Boost 1.87.0 is the first release whose bundled `qvm` includes it** (confirmed by comparing the pinned `qvm` submodule commit at each Boost release tag against the fix commit - 1.86.0 is behind it, 1.87.0/1.88.0/1.89.0 are all ahead of it).

I isolated this from the rest of the build to confirm precisely: compiling `quat_traits.hpp` standalone against the exact `qvm` commit Boost 1.86.0 bundles reproduces the error verbatim (same file, same lines, same columns); compiling it against the `qvm` commit Boost 1.87.0 bundles produces zero errors or warnings.

## Suggested fix

One line, in `cmake/boost.cmake`:

```diff
- URL "https://github.com/boostorg/boost/releases/download/boost-1.86.0/boost-1.86.0-cmake.tar.gz"
+ URL "https://github.com/boostorg/boost/releases/download/boost-1.89.0/boost-1.89.0-cmake.tar.gz"
```

(`find_package(Boost 1.86.0 ...)` immediately below doesn't need to change - it's a minimum-version check, and 1.89.0 satisfies it.)

1.87.0 is the *earliest* release that includes the fix (confirmed by comparing each release tag's bundled `qvm` submodule commit against the upstream fix commit - 1.86.0 predates it, 1.87.0/1.88.0/1.89.0 all postdate it), but I'd suggest going straight to 1.89.0, the current release, rather than the minimum - no reason to pin an intermediate version on purpose.

I confirmed this fully end-to-end, not just the isolated header, and not just one candidate version: with `third_party/JUCE` repointed at upstream JUCE 8.0.2 (the fix for #10), I built the full project against both 1.87.0 and 1.89.0 separately. Both complete with zero errors and zero `FAILED:` lines across the full build (1436 and 1457 steps respectively), and both produce a real, valid installed AU component (`Eclipsa Audio Renderer.component`, Mach-O arm64, verified with `file`). No other issues surfaced with either version once JUCE was also fixed.

Happy to open the `cmake/boost.cmake` PR if useful.

Start in cmake/boost.cmake, where the Boost archive URL is pinned, and review the existing find_package minimum-version requirement. Update the pinned release to a version containing the qvm fix, then perform a clean build with recent Clang and verify that the project completes without failures and produces the installed AU component.

Written by the indexing model from the issue text.