feat: add manage:list-external-buckets command

[jirkasemmler]

Changes:

• Adds manage:list-external-buckets, a read-only stack-wide audit of external buckets (buckets with hasExternalSchema). For each one it reports the created date, the isReadOnly flag, whether the bucket is linked from elsewhere, and whether KBC.description metadata is set.
• Documents it in the README next to storage:force-unlink-shared-buckets.

Written while investigating why descriptions were missing on older external buckets (DMD-1496), where the cause turned out to be isReadOnly on buckets created before that flag changed meaning. Keeping the command means the next person does not have to rebuild the query.

Implementation notes:

• Creates a 15-minute Storage token per project and drops it in a finally block, so a listing failure does not leak tokens.
• Projects the manage token cannot reach are reported and counted as skipped rather than aborting the run, which matters on stacks where not every project is accessible.
• De-duplicates projects that appear under more than one maintainer/organization.
• Writes CSV to stdout with the header projectId,projectName,bucketId,created,isReadOnly,linked,hasDescription,description, so it can be redirected straight to a file. Progress and summary lines are prefixed with #.

phpcs, phpstan (level 9), phpunit and a CLI boot check all pass. Not run against any real stack.

Split out of #106 — it is unrelated to the workspace tooling that PR consolidates.

---

Additional notes

⚠️ Don't forget to release new version after merge

[jirkasemmler]

tbh nevim kdo to chce, zaviram. si navajbi znova