Update LocalUserIndex changelog post 2.0.2008 release

[julianjelfs]

Marks the [unreleased] entry as released in 2.0.2008 (proposal 2327, executed 2026-08-06), and removes the moderation-referral-config compat shim which is no longer reachable (the old single-threshold shape only ever existed in pre-release test environments; all LUIs now run 2.0.2008).

🤖 Generated with Claude Code

[github-actions]

canbench 🏋 (dir: .)

./canbench_results.yml is up to date ✅

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Benchmark: add_reactions
  total:
    instructions: 1.38 B (0.00%) (change within noise threshold)
    heap_increase: 5 pages (no change)
    stable_memory_increase: 0 pages (no change)

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Benchmark: push_simple_text_messages
  total:
    instructions: 210.33 M (0.02%) (change within noise threshold)
    heap_increase: 12 pages (no change)
    stable_memory_increase: 0 pages (no change)

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