M1-T07: align docs to single-DB reality and re-export OpenAPI

Rewrite README (single app.db + one alembic_app chain, legacy data moved
once via scripts.migrate_legacy_data, accurate test list) and remove the
Grafana Provisioning section. Update architecture-overview to the unified
data layer (one Base, app-DB engine with WAL) and retire the
alembic_location / alembic_poo sections. Mark M1 done in the roadmap.
Re-export openapi/, which catches the spec up to the already-existing
/config/smtp/test and /public-ip/check endpoints (purely additive; M1's
DB-session dependency swap produced no schema change).

pytest 95 passed; ruff clean (pre-existing only); OpenAPI export idempotent.

openapi/openapi.json

@@ -249,6 +249,27 @@
         }
       }
     },
+    "/config/smtp/test": {
+      "post": {
+        "tags": [
+          "pages"
+        ],
+        "summary": "Smtp Test Submit",
+        "operationId": "smtp_test_submit_config_smtp_test_post",
+        "responses": {
+          "200": {
+            "description": "Successful Response",
+            "content": {
+              "text/html": {
+                "schema": {
+                  "type": "string"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/homeassistant/publish": {
       "post": {
         "tags": [
@@ -325,6 +346,27 @@
         }
       }
     },
+    "/public-ip/check": {
+      "get": {
+        "tags": [
+          "public-ip"
+        ],
+        "summary": "Run Public Ip Check",
+        "operationId": "run_public_ip_check_public_ip_check_get",
+        "responses": {
+          "200": {
+            "description": "Successful Response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/PublicIPCheckResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/ticktick/auth/start": {
       "get": {
         "tags": [
@@ -443,6 +485,36 @@
         "type": "object",
         "title": "HTTPValidationError"
       },
+      "PublicIPCheckResponse": {
+        "properties": {
+          "status": {
+            "type": "string",
+            "enum": [
+              "first_seen",
+              "unchanged",
+              "changed",
+              "error"
+            ],
+            "title": "Status"
+          },
+          "checked_at": {
+            "type": "string",
+            "format": "date-time",
+            "title": "Checked At"
+          },
+          "changed": {
+            "type": "boolean",
+            "title": "Changed"
+          }
+        },
+        "type": "object",
+        "required": [
+          "status",
+          "checked_at",
+          "changed"
+        ],
+        "title": "PublicIPCheckResponse"
+      },
       "StatusResponse": {
         "properties": {
           "status": {