feat(cli): support multiple sync folders in command-line account setup

[Unbrot]

Fixes #9966

Summary

• Allow repeated --localdirpath/--remotedirpath pairs so that multiple sync folders can be configured in a single CLI invocation
• When the account already exists, reuse it and add the new folders instead of aborting with an error
• Skip folders that are already configured (same local path + remote path) to make repeated invocations idempotent

Problem

Previously _localDirPath and _remoteDirPath were single QString members, so repeated flags silently overwrote each other. Additionally, a second invocation for the same account was rejected outright, making it impossible to add folders to an existing account via CLI.

During testing of the "repeated invocation for existing account" case, running the same command twice produced duplicate entries under the Multifolders settings group (indices 3 and 4 alongside the correct Folders\2 entry). This happened because the local directory is empty right after CLI setup (the sync journal is only written when the sync engine first runs), so the existing non-empty-directory guard did not catch the re-invocation. The result was two sync engines running against the same local and remote path simultaneously — causing redundant work and potential conflicts with no benefit.

Changes

• AccountSetupCommandLineManager: replaced _localDirPath/_remoteDirPath with QList<QString> accumulators; pairs are zipped and passed to the job
• AccountSetupFromCommandLineJob: constructor now accepts QList<QPair<QString,QString>>; existing accounts are reused rather than rejected; setupLocalSyncFolders iterates over all pairs; newly-created accounts are rolled back on failure but existing accounts are left intact
• AccountSetupFromCommandLineJob::setupLocalSyncFolders: before calling addFolder, check whether any existing folder already has the same cleanPath and remotePath; if so, log and skip — making the command idempotent

Test results

Single folder (--localdirpath ~/nc_test/1 --remotedirpath /test/f1): folder appears in config as Folders\0, exit 0. ✅

Multiple folders in one invocation (--localdirpath ~/nc_test/1 --remotedirpath /test/f1 --localdirpath ~/nc_test/2 --remotedirpath /test/f2): both folders appear in config (Folders\0, Folders\1), files synced correctly on both paths. ✅

Repeated invocation for existing account — new folder (--localdirpath ~/nc_test/3 --remotedirpath /test/f3 on an account already having f1/f2): folder added as Folders\2, account not deleted, exit 0. ✅

Repeated invocation for existing account — already-configured folder (same command run a second time): duplicate skipped with log message Folder … is already configured. Skipping., config unchanged, exit 0. ✅

Non-empty local folder: rejected with error before any account or folder is created. ✅

Missing --remotedirpath: defaults to /. ✅

🤖 Generated with Claude Code

[Unbrot]

Btw. I compiled the changes and tested them on linux fedora / kde plasma wayland - It worked. We need it for Autoprovisioning nc desktop in our company. Using the already existent logic may be a better solution, than to modify the config itself from outside, as i saw in some descriptions.
Best Regs, Daniel (thats me - a real person)

[Unbrot]

The test showed a small glitch: If the same remote and local folder was specified with another run, than it got appended as multifolder, which makes no sense at all. should be fixed now.

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