fix(core): route conductor/tasks runtime chatter through logger (#649) (#687)

Replace 84 bare print() calls in core/conductor.py and 2 in core/tasks.py with
logger.{info,warning,error,debug} mapped by intent — these leaked to the FastAPI
server's stdout, violating CLAUDE.md headless-core rules (#1, #3). Decorative
separators/leading whitespace stripped. runtime.py:1020/1091 left as-is (print()
inside docstring Example blocks, never executed); events.py left as-is (Rich
console, CLI-intended). CLI UX preserved via events.py milestones + the CLI's own
Rich summary. Adds an AST guard plus a caplog behavioral test; migrates 3
conductor tests from capsys to caplog.

Closes #649.

Author: frankbria