Add stdio support for EverythingServer sample (continues #950)

[FengFafa97]

Continues #950, fixes #889.

This picks up @asklar's branch splitting EverythingServer into
EverythingServer.Core / EverythingServer.Http / EverythingServer.Stdio,
rebases it onto current main, and fixes the build breaks that surfaced
from the rebase:

• EverythingServerExtensions.cs: SampleAsync's named parameter was
  renamed to chatOptions upstream; updated the call site.
• EverythingServer.Core.csproj: added the MCP9005 suppression
  (Sampling deprecated per SEP-2577) that EverythingServer.Http.csproj
  already had — it doesn't propagate across the project reference.
• EverythingServer.Http/Program.cs: restored the MCPEXP002 pragma
  around the experimental RunSessionHandler assignment, matching the
  original Program.cs and docs/experimental.md.
• launchSettings.json: removed trailing commas that broke JSON parsing
  and silently disabled both launch profiles.

Verification:

• dotnet build: 0 warnings, 0 errors.
• Manually ran both samples and completed a live MCP initialize
  handshake against each (stdio via piped JSON-RPC, HTTP via a direct
  POST to the Streamable HTTP endpoint).

Out of scope for this PR: main's Program.cs also gained new
sample content since @asklar's branch was cut (icon/ServerInfo metadata
showcase, explicit stateful SessionMode). Not ported here to keep this
PR focused on restoring a green build; happy to follow up separately.

Co-Authored-By: Claude Sonnet 5

[FengFafa97]

Hi @jeffhandley — an update on #950: This PR has been rebased onto the current main branch, conflicts have been resolved, and local builds are passing (both stdio and HTTP examples successfully complete the initial handshake). The PR's CI workflow is currently awaiting maintainer approval—could someone please take a look when convenient? I am happy to adjust the scope of work or hand it over if the team prefers to take it from here.

[FengFafa97]

Hi @halter73 and @jeffhandley — this part is ready for review. This is the version @asklar split off from #950 and rebased onto the current main branch; my own changes are included in commit 5a080c1 (affecting 4 files, +8/−3), primarily fixing build failures caused by the rebase. The branch is synced with main, dotnet build succeeds, the local test suite passes, and both stdio and HTTP samples complete the initial handshake successfully. The associated workflows are currently awaiting approval. I am happy to adjust the scope as needed, or to hand over the work if you would prefer to take it from here.