EVM-side v2 announcer schema for parity with Stellar v2

[truthixify]

Tier: L (1-2 weeks) Type: feature

Context

Stellar's v2 announcer (#41) uses indexed event topics to let RPC providers filter by view-tag bucket server-side, cutting scan bandwidth ~256x. EVM still uses the v1 schema and pays the full cost. Need an EVM WraithAnnouncerV2 with equivalent topic indexing.

Scope

• New Solidity contract WraithAnnouncerV2.sol
• Indexed event params: schemeId, viewTagBucket, metadataKind
• Non-indexed: stealthAddress, ephemeralPubKey, metadata
• Deploy alongside v1 (do not replace)
• SDK follow-up: filtered getLogs calls

Acceptance criteria

• Contract + tests
• Deploy script updated
• Subgraph schema updated (Goldsky)
• SDK follow-up issue filed for EVM v2 filter consumption

Files to start with

• evm/contracts/ERC5564Announcer.sol
• stellar/EVENT_TOPIC_DESIGN.md (design rationale)
• stellar/stealth-announcer/src/lib.rs (Stellar v2 reference)

[truthixify]

Closing as out of scope for the Stellar Drips Wave. This wave is Stellar-only across contracts and sdk. Cross-chain / Solana / EVM / CKB / Hedera / Sui work would be welcome in a different round, but is not part of this wave's focus.

A replacement Stellar-focused issue will go up shortly to keep the per-repo issue count in range.