feat: project-orchestrator — engine@v0.1.0 submodule, PO config, fleet.toml registry, mgmt scripts, docs, Nix

The PO is itself a project using the agent-orchestrator harness (engine/ submodule pinned at
v0.1.0). Adds: agents.toml (one persistent fleet-management agent) + prompts/; fleet.toml (the
sole project<->harness<->ref registry) + docs/fleet-registry.md; scripts/ (fleet.py +
create/start/stop/update-project.sh); docs/manage-projects.md + docs/bootstrap.md; flake.nix/.lock
devShell (python311+tmux+git); README.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/_resolve.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# _resolve.sh — shared helper: given a fleet project name, echo "<location>\t<config>\t<harness>".
+# Sourced by start/stop/update scripts. Reads the PO's fleet.toml (the only project↔location record).
+set -euo pipefail
+PO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+resolve_project() {
+  local name="$1"
+  python3 - "$PO_ROOT/fleet.toml" "$name" <<'PY'
+import sys, tomllib
+path, name = sys.argv[1], sys.argv[2]
+with open(path, "rb") as f:
+    raw = tomllib.load(f)
+for p in raw.get("project", []):
+    if p.get("name") == name:
+        print("\t".join([p.get("location", ""), p.get("config", "agents.toml"), p.get("harness", "")]))
+        sys.exit(0)
+sys.exit(f"_resolve: no project named {name!r} in {path}")
+PY
+}