fix(proto): carry project match in remote search

[upsetbit]

Summary

Fixes #300.

• adds project_match to SearchRequest so remote search can carry explicit --project
• maps CLI explicit project scope into the remote search request
• applies the server-side substring filter across project path, remote, and marker
• covers request construction and server search filtering with tests

Validation

• go test ./internal/cli -run 'TestResolveProjectScopeExplicitProject|TestRunSearchRemoteAppliesExplicitProject|TestSearchLimit' -count=1\n- go test ./internal/server/handlers -run TestSessionsSearchProjectMatchFiltersPathRemoteOrMarker -count=1\n- go test ./...\n- just gen-check\n- go build -o ./bin/prosa ./cmd/prosa