The indexer's storage location was the `home` field of IndexerConfig, used only to derive the RocksDB dir. Defaulting to "." meant it landed in the process CWD — fine for the standalone service, but wrong when the indexer runs embedded in a logos_host subprocess (RocksDB ended up in an arbitrary/unwritable dir). Storage location is an operational concern the host should own, not something baked into a user-editable config.
Remove `home` from IndexerConfig and pass the storage directory explicitly:
- core: `IndexerCore::new(config, storage_dir)` derives `<storage_dir>/rocksdb`.
- ffi: `start_indexer(runtime, config_path, storage_dir)`; null/empty storage_dir falls back to ".". Lets a host (e.g. a Logos module's instance persistence path) own where state lives.
- service: `run_server(config, storage_dir, port)` + a `--data-dir` flag (default ".") on the binary, preserving current behaviour.
- drop `home` from the committed indexer config JSONs and the test fixtures.
BREAKING CHANGE: `start_indexer` gains a `storage_dir` parameter and IndexerConfig no longer has a `home` field.
