feat: Phase 5 stabilization schedules and custodian path URIs

Add phase5_stabilization_check State Hub resolver with progress evidence
sinks, schedule projections for daily and closeout checks, custodian:// and
activity-core:// runtime path resolution, and Railiance mounts under /var/custodian.

src/activity_core/runtime_paths.py

@@ -0,0 +1,37 @@
+"""Resolve repo-relative runtime paths for Custodian-owned assets."""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+_DEFAULT_CUSTODIAN_ROOT = Path("/home/worsch/the-custodian")
+_DEFAULT_ACTIVITY_CORE_ROOT = Path("/etc/activity-core")
+
+_CUSTODIAN_SCHEME = "custodian://"
+_ACTIVITY_CORE_SCHEME = "activity-core://"
+
+
+def custodian_repo_root() -> Path:
+    raw = os.environ.get("CUSTODIAN_REPO_ROOT", "").strip()
+    return Path(raw).expanduser() if raw else _DEFAULT_CUSTODIAN_ROOT
+
+
+def activity_core_root() -> Path:
+    raw = os.environ.get("ACTIVITY_CORE_ROOT", "").strip()
+    return Path(raw).expanduser() if raw else _DEFAULT_ACTIVITY_CORE_ROOT
+
+
+def resolve_runtime_path(raw_path: str) -> Path:
+    """Map custodian:// and activity-core:// URIs to mounted runtime paths."""
+    value = str(raw_path or "").strip()
+    if not value:
+        return Path(value)
+
+    if value.startswith(_CUSTODIAN_SCHEME):
+        return (custodian_repo_root() / value.removeprefix(_CUSTODIAN_SCHEME)).resolve()
+
+    if value.startswith(_ACTIVITY_CORE_SCHEME):
+        return (activity_core_root() / value.removeprefix(_ACTIVITY_CORE_SCHEME)).resolve()
+
+    return Path(value).expanduser()