[SeanShaffer88]

What

Implements the next roadmap item: publish sqlite3.def and vec0.def export lists so non-MSVC toolchains (MinGW-w64, LLVM) can generate import libraries for the DLLs.

• sqlite3.def — 365 exports from the built x64 DLL (352 common + 13 Windows-only sqlite3_win32_* helpers; sqlite3_version marked DATA).
• vec0.def — the three sqlite-vec entry points.
• tools/gen_def.ps1 — generates a def from a DLL with dumpbin.
• tools/gen_def.sh — generates the same list from a shared library with nm (Linux/macOS).
• CI regenerates both defs from the built artifacts and fails on drift: Windows compares byte-for-byte, Linux compares symbol coverage (filtering the Windows-only helpers).
• The release workflow now runs the same fetch → build → defs → harness → shell-smoke gate as CI, and the zip includes sqlite3.exe, sqlite3.def, and vec0.def (the shell was previously built but not packaged).

Also

• Fixed the harness's vec_version() check, which was a no-op (|| 1 always passed). It is now a real assertion.
• Documented the defs in README, docs/FEATURES.md, ROADMAP, and AGENTS.
• Added .gitattributes so the generated defs and POSIX scripts keep LF endings on Windows checkouts (needed for the byte-for-byte comparison).

Verification

• Local Linux build of the pinned 3.54.1 amalgamation: harness passes 21/21 checks (including vec0 KNN).
• tools/gen_def.sh output matches the checked-in defs modulo the Windows-only symbols.
• Windows CI will verify the exact DLL export set; if the MSVC export table differs from the candidate list, the def comparison step will show it.

Roadmap

Marks the export-list candidate done; ICU and ARM64 remain as candidates.