Address PR review: backup correctness/security + drop hardening

Fixes from the code review of this branch:

- Backup requires a running container (it runs via `docker exec`, which
  can't run on a stopped one). Removed the misleading "Backup" button
  from the stopped-project actions, added an explicit running check with
  a clear error, and corrected the doc comment. (H1)
- jq sanitization fallback no longer leaks secrets: if ~/.claude.json
  can't be parsed, the backup substitutes an empty object and warns to
  stderr instead of copying the raw file (which held primaryApiKey /
  oauthAccount). Verified the raw key never reaches the archive. (H2)
- Dropped-file paths typed into the terminal are now always single-quoted
  (with '\'' escaping), not only when they contain whitespace — a name
  like `foo$(whoami).txt` was previously sent raw into the shell. (M2)
- write_bedrock_static_credentials checks the exec exit code via the new
  exec_oneshot_env_status and fails loudly on a write/chmod error instead
  of silently reporting success. exec_oneshot keeps its
  ignore-exit-code behavior so list_container_files is unaffected. (M4)
- Backup removes a partial/truncated archive on any stream error and
  treats a non-zero tar exit code as failure (a truncated gzip was
  previously reported as success). (L1)
- Dropped files are capped at 256 MiB to avoid ballooning host RAM
  (the file is read fully into memory then re-tarred). (M3)
- Stopped excluding .git/objects from the backup so git history,
  including unpushed commits, is preserved faithfully. (L3)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src-tauri/src/commands/terminal_commands.rs

@@ -202,6 +202,17 @@ pub async fn upload_host_file_to_terminal(
         return Err(format!("{} is a directory — drop individual files", host_path));
     }
 
+    // Guard against ballooning host RAM: the file is read fully into memory and
+    // then re-packed into an in-memory tar, so cap the size of a dropped file.
+    const MAX_DROP_BYTES: u64 = 256 * 1024 * 1024; // 256 MiB
+    if meta.len() > MAX_DROP_BYTES {
+        return Err(format!(
+            "File too large to drop into the terminal ({:.0} MB; limit {} MB). Mount it into the project or use the Files panel instead.",
+            meta.len() as f64 / (1024.0 * 1024.0),
+            MAX_DROP_BYTES / (1024 * 1024)
+        ));
+    }
+
     let data =
         std::fs::read(&host_path).map_err(|e| format!("Failed to read {}: {}", host_path, e))?;