fix: make webhooks and price trackers network-aware (#188)

[Ingenious-02]

Summary

Closes #188

Fixes the dual-network seam where price trackers and webhooks were network-blind:

1. Network-scoped lastPrice maps: Keyed module-level lastPrice maps in src/ingesters/sdex.ts, src/ingesters/amm.ts, src/ingesters/soroswap.ts, and src/ingest/venues/aquarius.ts by (network, pairKey) rather than pairKey alone. A tick on testnet now never pollutes or supplies the "previous price" for a mainnet threshold crossing (and vice versa).
2. Network-aware webhook dispatching: Updated dispatchPriceUpdate in src/webhookDispatcher.ts to accept network and filter webhooks specifically by the network that emitted the price event, rather than filtering by the process's activeNetwork.
3. Network-aware ingester dispatch: All ingesters (sdex, amm snapshot + trades, soroswap, and aquarius) now forward their active network into dispatchPriceUpdate.
4. Network-aware webhook subscription: POST /webhooks now supports explicit network selection from req.body.network (validated against allowed networks), falling back to req.network or activeNetwork.
5. Fixed AMM pool snapshot network tag: In src/ingesters/amm.ts, snapshotPool was writing network: activeNetwork to prisma.poolSnapshot.create, now properly tags with the network parameter.

Acceptance Criteria Verification

• A tick on one network never supplies the previous price for the other: Verified in src/__tests__/dualNetworkAlerts.test.ts.
• A webhook fires for the network whose event triggered it: Verified in src/__tests__/dualNetworkAlerts.test.ts and src/__tests__/webhooks.test.ts.
• A test drives both networks through the same pair and asserts the alerts do not cross: Tested across SDEX, AMM, Soroswap, and Aquarius with interleaved trades on the same pair.
• No remaining module-level price state is keyed by pairKey alone: All in-memory lastPrice state is keyed by ${network}:${pairKey}.

Test Verification

• All 48 test files (411 passing tests) pass cleanly.
• npx tsc --noEmit passes with 0 errors.

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