Use pointer semantics for entity update inputs (SDK v0.2.15)

[chrisghill]

What

Bumps the massdriver-sdk-go dependency and updates the project, environment,
and component update commands to match the SDK's new UpdateInput shape.

The SDK changed UpdateInput.Name / Description from string to *string
(and added *bool fields elsewhere) so it can distinguish an unset field
from an intentionally empty one. A nil pointer / nil map now means "leave
this value unchanged at the server."

Changes

• Bump SDK to v0.2.15 (needed for mass whoami; also brings the pointer-based
  update inputs).
• Only send changed fields. Each update command now sets a field on UpdateInput
  only when its flag was explicitly passed (cmd.Flags().Changed(...)), letting nil
  signal "unchanged."
• Drop the pre-update Get + backfill. Previously each command fetched the current
  entity and re-sent every existing value so unset flags wouldn't blank the field. The
  server now handles the merge, so this extra round-trip is gone.
• Reject no-op updates. Running an update with no flags now errors with
  nothing to update: set at least one of --name, --description, or --attributes
  instead of silently making a meaningless API call that reported success.

Why it matters

Before the pointer change, an argument-less update would have blanked name/description
at the server — the old backfill fetch masked that. With the fetch removed, the explicit
guard makes the "nothing to update" case a clear error rather than a misleading
"✅ updated".

Testing

• go build ./... and go vet ./cmd/ pass.