fix(server): keep discover lifecycle bootstrap-neutral

[faisal-shah]

Summary

• keep metadata-bearing server/discover requests bootstrap-neutral
• select the classic lifecycle on a subsequent initialize
• select the inline lifecycle only on the first valid ordinary metadata-bearing request
• leave malformed and unsupported bootstrap requests recoverable
• enqueue the lifecycle-selecting inline request into the normal service loop so bidirectional handlers remain safe

Verification

• cargo test --package rmcp --features "client transport-io macros schemars"
• cargo clippy --package rmcp --features "client transport-io macros schemars" --lib --test test_server_initialization --test test_stateless_server_requests --test test_subscriptions -- -D warnings

[tenequm]

We hit this in production: Claude Code sometimes opens a stdio session with a bare tools/list (no _meta). On 3.5.0 the server answers -32602 and then exits, so the client never falls back to initialize. This PR fixes it for us. Any chance of moving it forward? Happy to help address the review comments.

[DaleSeo]

@faisal-shah Since a user is hitting this in production, I went ahead and pushed the review fixes.

@tenequm We'll include this fix in the next release.