acpctl create session should support -f/-F to stream output after creation

[jeremyeder]

Problem

acpctl create session returns immediately after creation. To see output, users must copy the session ID and run a second command:

acpctl create session --name test --prompt "hello" --repo-url https://github.com/...
# returns ID, then manually:
acpctl session messages <id> -F

Proposed Solution

Add -f and -F flags to create session that create the session and immediately begin streaming messages:

acpctl create session --name test --prompt "hello" -F

• -f — stream until turn ends (matches session messages -f behavior)
• -F — continuous follow until Ctrl+C (matches session messages -F behavior)

Should reuse the existing session messages streaming logic.

Context

Tracked internally as platform-dab. Related to #1575 (--name/--latest on session messages), which together would make the CLI workflow much smoother.