add markdownlint config and fix README lint errors

Add .markdownlint.json with 120-column line limit.
Fix MD060 table separator style to match padded header rows.

.markdownlint.json

@@ -0,0 +1,7 @@
+{
+  "MD013": {
+    "line_length": 120,
+    "tables": false,
+    "code_blocks": false
+  }
+}

README.md

@@ -33,7 +33,7 @@ nodes:
 ## Configuration
 
 | Env Variable | Default | Description |
-|--------------|---------|-------------|
+| ------------ | ------- | ----------- |
 | `ROBOT_IP` | `192.168.1.192` | Robot IP address |
 | `DEFAULT_SPEED` | `30` | Movement speed (mm/s) |
 | `DEFAULT_UNITS` | `mm` | Position units (mm or m) |
@@ -61,7 +61,7 @@ Access at `http://localhost:8080/`
 Interactive docs at `http://localhost:8080/docs`
 
 | Method | Endpoint | Description |
-|--------|----------|-------------|
+| ------ | -------- | ----------- |
 | GET | `/` | Web control interface |
 | GET | `/api/status` | Robot status (connected, errors) |
 | GET | `/api/pose` | Current TCP pose |
@@ -76,7 +76,7 @@ Interactive docs at `http://localhost:8080/docs`
 ### Vacuum Gripper (when `VACUUM_ENABLED=true`)
 
 | Method | Endpoint | Description |
-|--------|----------|-------------|
+| ------ | -------- | ----------- |
 | GET | `/api/vacuum` | Get vacuum status |
 | POST | `/api/vacuum/on` | Turn vacuum on |
 | POST | `/api/vacuum/off` | Turn vacuum off |