ci(distributed): run the distributed e2e suite on PRs

The suite has never run in CI, so 239 specs across 32 files were verified only
by hand. Path-filtered to distributed code, advisory until it earns a track
record, and with flake retries at 1 rather than 5 so nondeterminism surfaces
instead of being retried away.

Assisted-by: Claude Opus 5 [claude-code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
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