fix: remove PROMPT.md files — formulas are the source of truth (#12)

- Delete gardener/PROMPT.md (dust-vs-ore rules already in run-gardener.toml)
- Delete supervisor/PROMPT.md (content covered by run-supervisor.toml;
  migrate unique "Learning" section into formula's journal step)
- Delete vault/PROMPT.md and create formulas/run-vault.toml as the
  source-of-truth formula for vault action classification/routing
- Update supervisor/supervisor-poll.sh to read from formula instead of PROMPT.md
- Update vault/vault-agent.sh to read from formula instead of PROMPT.md
- Update supervisor/AGENTS.md, vault/AGENTS.md, README.md references

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

supervisor/AGENTS.md

@@ -32,7 +32,6 @@ runs directly from cron like the planner and predictor.
   health-assessment, decide-actions, report, journal) with `needs` dependencies.
   Claude evaluates all metrics and takes actions in a single interactive session
 - `$OPS_REPO_ROOT/journal/supervisor/*.md` — Daily health logs from each supervisor run
-- `supervisor/PROMPT.md` — Best-practices reference for remediation actions
 - `$OPS_REPO_ROOT/knowledge/*.md` — Domain-specific remediation guides (memory,
   disk, CI, git, dev-agent, review-agent, forge)
 - `supervisor/supervisor-poll.sh` — Legacy bash orchestrator (superseded by