fix: Migrate planner, predictor, supervisor to SDK (#6)
Replace tmux-based run_formula_and_monitor() with synchronous agent_run()
from lib/agent-sdk.sh, matching the pattern established in gardener-run.sh.
Key changes per agent:
- Drop agent-session.sh, use agent-sdk.sh (SID_FILE, LOGFILE)
- Remove SESSION_NAME, PHASE_FILE, PHASE_POLL_INTERVAL (tmux/phase artifacts)
- Strip phase protocol from prompt footer (SDK mode needs no phase signals)
- Preserve all prompt composition: context blocks, memory, journal, preflight
Shared helpers added to lib/formula-session.sh:
- build_sdk_prompt_footer(): build_prompt_footer minus phase protocol
- formula_worktree_setup(): fetch + cleanup + create worktree + EXIT trap
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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