feat: Discard all, claude-style image pastes, large local drops, per-account / list

- Changes panel: **Discard all** beside Commit discards every non-conflicted
  file in one `discard`, after a dialog naming how many untracked files go.
- Terminal: a `claude` pane gets dropped/pasted images as bare paths (shown as
  `[Image #n]`) and other files as `@` mentions (`claudePastes`); a local
  browser's copied `file://` paths and text-drag file lists paste by path.
- `POST /api/run/drop-file`: a loopback browser outside server mode may drop
  up to 2 GB, streamed to disk; remote stays 20 MB.
- cc-config skills/commands/plugins read the USER scope of the account the
  pane runs as (S3 member home by `cwd`), never another user's or the host's
  for a non-admin without an account; the run form passes its cwd to plugins.

client/src/lib/promptAttach.ts

@@ -169,6 +169,22 @@ export function claudeMention(path: string): string {
   return /\s/.test(p) ? `@"${p}"` : `@${p}`;
 }
 
+const IMAGE_PATH = /\.(png|jpe?g|gif|webp)$/i;
+
+/** What a terminal pastes for files dropped or pasted on a `claude` pane, one
+ *  paste per entry, as a local terminal hands them over: the images as their
+ *  bare paths, each a paste of its own — the shape Claude Code turns into
+ *  `[Image #n]`, as it does a native drop — and every other file as an `@`
+ *  mention, together in one. A Windows path, or
+ *  one with a space, stays a mention — the bare path stayed plain text there
+ *  (see `claudeMention`). */
+export function claudePastes(paths: string[]): string[] {
+  const bare = (p: string) => IMAGE_PATH.test(p) && p.startsWith("/") && !/\s/.test(p);
+  const images = paths.filter(bare);
+  const others = paths.filter((p) => !bare(p)).map(claudeMention);
+  return [...images, others.join(" ")].filter(Boolean);
+}
+
 export const SKILL_MIME = "application/x-agenthub-skill";
 // A skill's name as Claude Code types it: `name` or `plugin:name`.
 const SKILL_RE = /^[\w.-]+(?::[\w.-]+)?$/;