fix(build): apply patches on pipefail, dedupe optimum types in donor csproj

[dxcvvxd]

fixes #94, #90, #96

fix 1 (issue #94 & #90): csproj owned by both sources/ overlay and old patches/ file

• sources/VintagestoryApi/VintagestoryAPI.csproj overlay now canonical owner of donor csproj.
• delete stale patches/VintagestoryApi/VintagestoryAPI.csproj.patch, its 2 <Compile Remove> lines merged into overlay.
• one file, one owner. bootstrap no longer dies on ownership-conflict check.

fix 2 (issue #96, first part): patch gate die on sigpipe

• bootstrap runs set -o pipefail. gate find "$patches_dir" -name '*.patch' -print | head -n 1 | grep -q .. head exits after first line, find gets SIGPIPE (141), pipeline fails, else branch runs. "No patches/ to apply." every run.
• fix: find "$patches_dir" -name '*.patch' -print -quit >/dev/null 2>&1. -quit stops find after first match, no broken pipe. all 118 patches apply.

fix 3 (issue #96, second part): cs0433 same type in two dll

• overlay csproj removed 18 of 21 Optimum files from donor compile. missed 3: OptimumCompatibilityGuard, OptimumFrustumCullSimd, OptimumKometGuard.
• those, plus OptimumMeshPartPool and OptimumChunkVisibilityBfs (taken from deleted patch), compiled into both VintagestoryAPI.dll and Optimum.Api.Contracts.dll, so mods referencing both get cs0433.
• add all 5 missing <Compile Remove> entries to overlay. Optimum types compile only in contracts.

verify

• make refresh prints "Patches: 118 applied, 0 skipped, 0 failed"
• dotnet build VintageStory.slnx -c Release succeeds, 0 errors
• dotnet test passes 1042 tests