feat(06-02): add sftp entry to registry, index, and rclone-conf

- Add sftp entry to BACKEND_REGISTRY with host, user, pass, key_pem fields
- Remove placeholder NOTE comment (sftp entry now present)
- Add sftp, onedrive, gcs, b2 to BACKEND_SCHEMAS in index.ts
- Add sftp, onedrive, gcs (google cloud storage), b2 to RCLONE_TYPE_MAP
- All 55 registry and rclone-conf tests pass; zero TypeScript errors

src/schemas/registry.ts

@@ -16,9 +16,6 @@ export interface FieldDef {
   options?: { value: string; label: string }[]; // for inputType: 'select'
 }
 
-// NOTE: 'sftp' entry is intentionally missing — Plan 02 (06-02-PLAN.md) adds it.
-// The type cast below suppresses the incomplete-record error until that plan runs.
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
 export const BACKEND_REGISTRY = {
   azureblob: {
     displayName: 'Azure Blob Storage',
@@ -180,6 +177,41 @@ export const BACKEND_REGISTRY = {
       },
     ],
   },
+  sftp: {
+    displayName: 'SFTP',
+    description: 'SSH File Transfer Protocol',
+    fields: [
+      {
+        key: 'host',
+        label: 'Host',
+        inputType: 'text',
+        required: true,
+        placeholder: 'sftp.example.com',
+        helpText: 'The SSH server hostname or IP address',
+      },
+      {
+        key: 'user',
+        label: 'Username',
+        inputType: 'text',
+        required: true,
+        placeholder: 'admin',
+      },
+      {
+        key: 'pass',
+        label: 'Password',
+        inputType: 'password',
+        required: false,
+        helpText: 'SFTP password. Note: rclone may require the password to be obscured using `rclone obscure <password>`. If authentication fails, use the obscured value instead of the plain password.',
+      },
+      {
+        key: 'key_pem',
+        label: 'Private Key (PEM)',
+        inputType: 'password',
+        required: false,
+        helpText: 'Paste your private key in PEM format (-----BEGIN ... PRIVATE KEY-----)',
+      },
+    ],
+  },
   b2: {
     displayName: 'Backblaze B2',
     description: 'Backblaze B2 Cloud Storage',