Add seat allocation table to subscriptions docs

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Patch merge may need examples. Add a table for managing seats (e.g., assign/unassign) tied to Unique Instance ID from legal/.

What needs to be done

• Add table with steps.

Labels: ~"group::documentation" ~"technical writing" ~"size::1"

Target MD File(s): doc/subscriptions/seats.md.

MR Guidance

1. Branch: git checkout -b subscriptions-seats-table.
2. Edit: Table linking to legal ID.
3. Commit: git commit -m "Add seat management table\n\nCloses #YOUR_ISSUE_ID".
4. MR: Label subscriptions.