Batch sender fixed2

[stpatrickghost]

Summary

Batch-sender was still emitting a single-topic ("ANNOUNCE",) event, so indexers could not apply server-side topic-3 view-tag filtering to anything sent through it.

This change routes each batch-sender transfer through the announcer contract, the same pattern stealth-splitter already uses. Announcements now use the v2 4-topic layout:

topics: ("announce", scheme_id, view_tag_bucket, metadata_kind)
data: (stealth_address, ephemeral_pub_key, metadata)

view_tag_bucket = metadata[0] as u32.

Issue #62 is an audit-doc correction only. Splitter fund_split already calls announcer_client::announce. No splitter code change.

Changes

• stealth-batch-sender batch_send now invokes stealth-announcer per transfer
• Transfer includes metadata; ephemeral_pub_key must be exactly 32 bytes
• Unit + snapshot tests assert the 4-topic v2 layout
• New integration test topic_filter.rs checks topic-3 filtering across announcer, splitter, and batch-sender
• EVENT_INDEXING_AUDIT.md closes Per-network deployment config validation #63 and corrects the stale Independent third-party audit preparation pack #62 splitter verdict
• Reference indexer processor.ts uses one announcement decoder for all three sources (no batch-sender-specific single-topic path)

Acceptance

• Batch-sender emits the 4-topic layout in unit + snapshot tests
• Integration test verifies topic-3 filter returns only matching view-tag entries across all three sources
• EVENT_INDEXING_AUDIT.md closes Per-network deployment config validation #63 and corrects Independent third-party audit preparation pack #62 (splitter already routes through announcer)
• Reference indexer treats announcer, splitter, and batch-sender uniformly

Test plan

• cargo test -p stealth-batch-sender
• cargo test -p integration-tests --test topic_filter
• cargo test -p integration-tests --test chaos
• cargo fmt --all --check

Closes #159

[stpatrickghost]

@truthixify, please review and merge.

[truthixify]

Merged @stpatrickghost. Opening a fresh branch was the right call once #175 rewrote batch-sender underneath the old one; untangling that rebase would have cost more than starting clean. Thanks for sticking with it through three rounds.