fix(cli): ignore and clean up folders left with only +types

[benatespina]

Summary

• Deleting or renaming an aggregate or a read model left its generated +types behind. The next bounda generate took that folder for a module, failed with "a read model needs a view.ts with its fields" and stopped before removeOrphans could clean it up, so the app would not start until someone deleted the folder by hand.
• Discovery now skips a folder that holds nothing but +types (and Finder's .DS_Store), at any depth, and the run removes those files along with the folders it empties.

Changes

• discover.ts: list() leaves out directories that contain only +types directories, recursively. This applies at every level: aggregates, read models, projections/<aggregate>/, commands/, and so on, which also keeps a leftover aggregate out of the set used to check projection and process folders.
• .DS_Store does not count: on macOS Finder drops one into every folder it opens, which would otherwise bring the failure back. A folder with only a .DS_Store is still reported.
• write.ts: removeOrphans also removes a directory once removing orphans has emptied it, .DS_Store aside. A folder that was already empty belongs to the user and stays, and the app directory is never removed.
• Tests for both: leftovers ignored at any depth; an empty folder, or one with anything next to +types, is still reported; emptied folders pruned while pre-existing empty ones stay.
• docs/reference/cli.md and a patch changeset for @bounda-dev/cli.

Key Features

• A stale +types tree no longer blocks bounda generate, --watch or the Vite plugin.
• Folders the user created and has not filled yet still get the usual convention error.

Quality

• pnpm check green.
• Stryker on @bounda-dev/cli: discover.ts 95.74 %, write.ts 95.65 %. No surviving mutant is in the new logic; the one at write.ts:81 is equivalent, since walking a file reads it as empty.