fix: honor --stream true for nullable request flags

[fallintoplace]

Problem

Ten streaming commands model the request field as requestflag.Flag[*bool] so they can represent unset, true, false, and null. The command branch used cli.Command.Bool, which only recognizes a concrete bool. As a result, passing --stream true still selected the non-streaming SDK method.

The two response retrieval commands use concrete boolean flags and are unaffected.

Fix

• add requestflag.FlagBool to read both bool and *bool values safely
• route all ten affected create, submit, edit, and generate handlers through it
• preserve nullable request serialization, including explicit null

Coverage

• unit coverage for concrete booleans, pointer booleans, nil, and unknown flags
• end-to-end SSE coverage for every affected command shape
• explicit --stream null coverage for the non-streaming path
• a held-open SSE response that verifies the rendered event arrives before the response completes

Validation

• ./scripts/test
• go test -race ./internal/requestflag ./pkg/cmd -run "^(TestFlagBool|TestNullableStreamFlags)$" -count=1
• go vet ./...
• ./scripts/lint