Add shared file storage with folder tree, permissions, and file manager UI

New document hub for centralized file storage — replaces scattered
drives and USB sticks for non-technical SMBs. Three new tables:
storage_folder (nested hierarchy), storage_folder_permission (role
and user-level access control), storage_file.

Backend: folder CRUD with nested paths, file upload/download via
signed URLs, permission checks (view/edit/admin with inheritance
from parent folders), public/private toggle, breadcrumb navigation,
file search.

Frontend: two-panel file manager — collapsible folder tree on left,
icon grid view on right. Folder icons by type, file size display,
upload button, context menu for download/delete. Breadcrumb nav.
Files sidebar link added.

packages/backend/src/db/migrations/0022_shared_file_storage.sql

@@ -0,0 +1,32 @@
+CREATE TYPE "storage_folder_access" AS ENUM ('view', 'edit', 'admin');
+
+CREATE TABLE "storage_folder" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "parent_id" uuid,
+  "name" varchar(255) NOT NULL,
+  "path" text NOT NULL DEFAULT '/',
+  "created_by" uuid REFERENCES "user"("id"),
+  "is_public" boolean NOT NULL DEFAULT true,
+  "created_at" timestamp with time zone NOT NULL DEFAULT now(),
+  "updated_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+CREATE TABLE "storage_folder_permission" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "folder_id" uuid NOT NULL REFERENCES "storage_folder"("id") ON DELETE CASCADE,
+  "role_id" uuid REFERENCES "role"("id"),
+  "user_id" uuid REFERENCES "user"("id"),
+  "access_level" "storage_folder_access" NOT NULL DEFAULT 'view',
+  "created_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+CREATE TABLE "storage_file" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "folder_id" uuid NOT NULL REFERENCES "storage_folder"("id") ON DELETE CASCADE,
+  "filename" varchar(255) NOT NULL,
+  "path" varchar(1000) NOT NULL,
+  "content_type" varchar(100) NOT NULL,
+  "size_bytes" integer NOT NULL,
+  "uploaded_by" uuid REFERENCES "user"("id"),
+  "created_at" timestamp with time zone NOT NULL DEFAULT now()
+);

packages/backend/src/db/migrations/meta/_journal.json

@@ -155,6 +155,13 @@
       "when": 1774810000000,
       "tag": "0021_remove_company_scoping",
       "breakpoints": true
+    },
+    {
+      "idx": 22,
+      "version": "7",
+      "when": 1774820000000,
+      "tag": "0022_shared_file_storage",
+      "breakpoints": true
     }
   ]
 }