Keep the IndexedDB bootstrap below the MSVC literal limit

[wieslawsoltes]

Parent capability: #56
Release epic: #227

Reproduction

The required Windows x64 runtime-package job fails on current main 70a2db4c in run 35254142552, job 105313709988:

webscene_indexeddb_compatibility.h(431,1): error C2026: string too big, trailing characters truncated

The same error predates #298 and reproduces in the PR #300 post-merge run 35252631301. #298's new FetchEvent bootstrap no longer emits its former C2026 after being split; the remaining diagnostic names only the IndexedDB bootstrap.

Required fix

• Preserve the IndexedDB JavaScript source byte-for-byte while representing it as bounded compile-time parts below MSVC's literal limit.
• Join parts once per realm without changing evaluation order, source URL, errors, or storage semantics.
• Extend the fail-closed bootstrap extractor/portability contract so no generated or handwritten native bootstrap can silently exceed the MSVC bound again.
• Do not weaken the runtime-package job or disable IndexedDB on Windows.

Acceptance

• Exact source length and SHA-256 match before/after the representation change.
• Portable bootstrap contract and native IndexedDB contracts pass.
• Windows x64 runtime-package compile advances past webscene_indexeddb_compatibility.h; no C2026 remains in the exact job log.
• Existing macOS/Linux IndexedDB open/upgrade/transaction/restart gates remain unchanged.
• Record compile/runtime cost and prove no retained allocation across repeated realm creation/teardown.

[wieslawsoltes]

Focused implementation is open as PR #307 at aee9cb07, rebased onto 50443f5b.

The single 19,859-byte IndexedDB raw literal is now two adjacent 7,963-byte and 11,896-byte tokens. The compiled std::string_view retains the exact source SHA-256 a3c907644e9b6c9d63eddfbd6a591802e99bbd3249a3b1437788ce4eb1c73b64.

Direct evidence:

• Windows 11 ARM64 Parallels VM, Visual Studio 2026 Build Tools: MSVC /std:c++20 /W4 /WX exact-header compile passed;
• portable bootstrap literal contracts pass 3/3 after the Stream and cache admitted Code OSS webview resources #266 stack rebase;
• extracted JavaScript passes Node syntax validation;
• AppleClang strict header compile and 19,859-byte static assertion pass.

The Windows NuGet runtime build is the only hosted merge gate being retained; unrelated queued lanes were cancelled.