feat: launch ingesters per enabled network in the bootstrap (#117)

[gideonpius7-design]

Summary

src/index.ts previously started exactly one instance of each of the five venue ingesters (SDEX, AMM, Soroswap, Snapshot, Aquarius), always bound to whatever network was active at startup. To index more than one network in the same process, each ingester now runs once per enabled network.

The per-network client factories (#139) and per-network venue config (#138) this builds on are already on main, so this diff is just the orchestration change.

Changes

• src/network/enabledNetworks.ts (new): getEnabledNetworks() reads the comma-separated ENABLED_NETWORKS env var (e.g. testnet,mainnet), trims, lowercases, dedupes, and filters to known network names. When unset — or when nothing valid remains after filtering — it falls back to just the currently active network (STELLAR_NETWORK), so a single-network deployment starts exactly one instance of each ingester rather than one per network.
• src/index.ts: loops over the enabled networks and starts SDEX, AMM, Soroswap, Snapshot, and Aquarius once per network. restartIngester's retry closure now captures the specific (venue, network) pair, so a crash in, say, Soroswap on mainnet only restarts that one instance and cannot affect the ingesters running on testnet.
• src/ingesters/snapshot.ts: appendSnapshots() / startSnapshotIngester() now take a network argument. price_snapshots rows are network-scoped via the (network, pair, ts) primary key, so a single shared instance could only ever snapshot the active network — each enabled network now gets its own loop.
• src/ingest/venues/aquarius.ts: startAquariusIngester() / ingestAquariusPair() take a network argument and resolve the per-network Aquarius block via getNetworkConfig(network) (enabled flag + API URL).
• .env.example: documents ENABLED_NETWORKS.
• src/__tests__/enabledNetworks.test.ts (new): covers the default fallback, explicit multi-network lists, whitespace/casing normalization, deduplication, and filtering out unrecognized network names.

Acceptance criteria (#117)

• Each ingester runs once per enabled network
• Restart logic isolates per-network instances (restartIngester keyed on (venue, network))
• Single-network mode still starts five loops, not ten (ENABLED_NETWORKS unset → [activeNetwork])

Testing

• npx tsc --noEmit passes
• npx vitest run passes — 312 passed, 1 skipped (7 new tests in enabledNetworks.test.ts)

closes #117

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