fix(extraction): preload the Objective-C grammar for C-family headers (#1628) (#1781)

Land upstream PR #1634 by @maxmilian, commit
8d398a92e30c9df27196bc90833efd674384569d.

Path-only detection classifies .h files as c, so preloading previously
covered c and cpp but missed objc selected by content-aware detection.
Preload objc alongside cpp whenever c is present. Full indexing and
changed-file reindexing now share preloadLanguagesForFiles().

Retain all four upstream unit tests and place the existing #1628 changelog
entry under Unreleased / Fixes / Symbols, tests and the viewer.

Verified fail -> pass on Linux with the reporter's repro.h as the only
source file, without a .m or .mm grammar seed. Before: Objective-C parser
initialization failure, 0 nodes, index state failed. After: Indexed 1 files,
2 nodes, 1 edge, index state complete; node CGRepro finds the class and
errors.log is absent.

Validation: npx tsc && npm run copy-assets passed; rebuilt CLI is executable.
npx vitest run __tests__/preload-languages.test.ts: 4 tests passed.

Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>
Co-authored-by: Max Hsu <maxmilian@gmail.com>

CHANGELOG.md

@@ -213,6 +213,8 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 #### Symbols, tests and the viewer
 
+- Objective-C headers now index in a project that has no `.m` file. A `.h` file is read as C from its name alone, and only later — once its contents are read — recognized as Objective-C; the grammar for that was never loaded up front, so the file failed with a parser error and nothing in it reached the index. Adding any `.m` file used to make the same header work, which is what made this look arbitrary. Thanks @Juddd. (#1628)
+
 - TypeScript interface methods and properties are now indexed, so `node`, `callers` and impact can find platform `.d.ts` APIs while declaration-only files keep their lower ranking on flow queries; re-index TypeScript projects after upgrading. (#1638)
 - Lua and Luau function expressions assigned to locals, table members, or keyed table fields are now indexed as callable nodes. Calls from `local f = function() ... end`, `M.f = function() ... end`, and callback tables such as `M.handlers = { onClick = function() ... end }` are attributed to the named function or method instead of collapsing onto the file node, so callers and impact no longer omit these handlers. Re-index after upgrading. (#1616, #1650)
 - **Functions bound with `const` inside another function are symbols now.** `const handleClear = () => {…}` inside a React component — every handler that skips `useCallback` — was invisible to `callers`, `callees` and impact, answering "Symbol not found" exactly the way a function with no callers would. It is indexed like its module-level twin, contained by the enclosing function, with its own calls. Re-index after upgrading. (#1669)