Enable trim analyzers and deterministic package metadata

[Widthdom]

Summary

• Enable trim/AOT analyzer warning surfaces for the CLI project, including per-site trimmer warnings.
• Enable deterministic build and Source Link metadata for the CodeIndex package project, with CI reproducibility flags and commit-date build metadata.
• Add bilingual changelog fragments for both issues.

Validation

• dotnet restore CodeIndex.sln --locked-mode
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet build CodeIndex.sln
• dotnet test CodeIndex.sln --no-build
• dotnet pack src/CodeIndex/CodeIndex.csproj --configuration Release --output .codex/tmp/pack-a
• dotnet pack src/CodeIndex/CodeIndex.csproj --configuration Release --output .codex/tmp/pack-b
• dotnet pack src/CodeIndex/CodeIndex.csproj --configuration Release --output .codex/tmp/pack-c -p:ContinuousIntegrationBuild=true -p:EmbedUntrackedSources=true
• dotnet pack src/CodeIndex/CodeIndex.csproj --configuration Release --output .codex/tmp/pack-d -p:ContinuousIntegrationBuild=true -p:EmbedUntrackedSources=true
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json

Notes

• Enabling Trim/AOT analyzer warnings unannotated; release builds risk silent reflection breakage #1598 intentionally surfaces existing IL2026/IL3050/IL207x trim and AOT warnings during builds.
• Two consecutive package archive hashes still differ because NuGet generates a random package/services/metadata/core-properties/*.psmdcp part name. Filed follow-up NuGet package archives still vary by generated core-properties part name #2756 for byte-for-byte archive normalization.

Documentation / Changelog

• DEVELOPER_GUIDE.md
• changelog.d/unreleased/1598.fixed.md
• changelog.d/unreleased/1602.fixed.md

Follow-Up

• NuGet package archives still vary by generated core-properties part name #2756

Fixes #1598
Fixes #1602