Harden runtime diagnostics for milestone 3

Make the milestone 3 runtime story predictable instead of treating doctor, self-check, and startup failures as loosely related surfaces.

Split doctor and self-check into distinct read-only flows, add tri-state diagnostic status with stable IDs and next steps, and reuse that wording in CLI output, service logs, and tray-triggered diagnostics. Add non-mutating config/model probes, a make runtime-check gate, and public recovery/validation docs for the X11 GA roadmap.

Validation: make runtime-check; PYTHONPATH=src python3 -m unittest discover -s tests -p 'test_*.py'; python3 -m py_compile src/*.py tests/*.py; PYTHONPATH=src python3 -m aman doctor --help; PYTHONPATH=src python3 -m aman self-check --help. Leave milestone 3 open in the roadmap until the manual X11 validation rows are filled.

src/aiprocess.py

@@ -34,6 +34,13 @@ class ProcessTimings:
     total_ms: float
 
 
+@dataclass(frozen=True)
+class ManagedModelStatus:
+    status: str
+    path: Path
+    message: str
+
+
 _EXAMPLE_CASES = [
     {
         "id": "corr-time-01",
@@ -748,6 +755,32 @@ def ensure_model():
     return MODEL_PATH
 
 
+def probe_managed_model() -> ManagedModelStatus:
+    if not MODEL_PATH.exists():
+        return ManagedModelStatus(
+            status="missing",
+            path=MODEL_PATH,
+            message=f"managed editor model is not cached at {MODEL_PATH}",
+        )
+
+    checksum = _sha256_file(MODEL_PATH)
+    if checksum.casefold() != MODEL_SHA256.casefold():
+        return ManagedModelStatus(
+            status="invalid",
+            path=MODEL_PATH,
+            message=(
+                "managed editor model checksum mismatch "
+                f"(expected {MODEL_SHA256}, got {checksum})"
+            ),
+        )
+
+    return ManagedModelStatus(
+        status="ready",
+        path=MODEL_PATH,
+        message=f"managed editor model is ready at {MODEL_PATH}",
+    )
+
+
 def _assert_expected_model_checksum(checksum: str) -> None:
     if checksum.casefold() == MODEL_SHA256.casefold():
         return