feat(web,server,core): attach files to a message from the composer (#121)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/web/src/lib/strings-en.ts

@@ -792,10 +792,17 @@ When done, open index.html in a browser and self-test once.`,
     },
     skillsBanner: (names: string[]): string =>
       `Using skill${names.length === 1 ? "" : "s"}: ${names.join(", ")}`,
-    /** Composer "+" extension menu (currently only goal mode; more entries later) and the goal chip. */
+    attachedFilesBanner: (names: string[]): string =>
+      `Attached file${names.length === 1 ? "" : "s"}: ${names.join(", ")}`,
+    /** Composer "+" extension menu (image upload, file attachment, goal mode) and the goal chip. */
     plusMenu: "More input options",
     uploadImage: "Upload image",
     uploadImageDesc: "Attach images to this message",
+    uploadFile: "Upload file",
+    uploadFileDesc: "Saved to the session scratchpad; the model reads them by path",
+    removeFile: "Remove file",
+    attachmentTooLarge: (name: string): string =>
+      `${name} exceeds the 10MB limit and was not attached.`,
     goalMode: "Goal mode",
     goalModeDesc: "Loop until the goal completes",
     goalBudgetLabel: "Token budget",
@@ -974,6 +981,7 @@ When done, open index.html in a browser and self-test once.`,
       unknown_skill: "This skill is not in the library.",
       file_not_found: "This file no longer exists.",
       file_too_large: "The file is too large.",
+      too_many_files: "Too many files attached to one message.",
       payload_too_large: "The request is too large.",
       dir_not_absolute: "The directory must be an absolute path.",
       not_a_dir: "That path is not a directory.",