refactor: split supervisor into infra + per-project, make poll scripts config-driven

Supervisor split (#26):
- Layer 1 (infra): P0 memory, P1 disk, P4 housekeeping — runs once, project-agnostic
- Layer 2 (per-project): P2 CI/dev-agent, P3 PRs/deps — iterates projects/*.toml
- Adding a new project requires only a new TOML file, no code changes

Poll scripts accept project TOML arg (#27):
- dev-poll.sh, review-poll.sh, gardener-poll.sh accept optional project TOML as $1
- env.sh loads PROJECT_TOML if set, overriding .env defaults
- Cron: `dev-poll.sh projects/versi.toml` targets that project

New files:
- lib/load-project.sh: TOML to env var loader (Python tomllib)
- projects/versi.toml: current project config extracted from .env

Backwards compatible: scripts without a TOML arg fall back to .env config.

Closes #26, Closes #27

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

review/review-poll.sh

@@ -6,7 +6,9 @@
 
 set -euo pipefail
 
-# Load shared environment
+# Load shared environment (with optional project TOML override)
+# Usage: review-poll.sh [projects/harb.toml]
+export PROJECT_TOML="${1:-}"
 source "$(dirname "$0")/../lib/env.sh"