Add README for state_admin_rules_cid schema and usage

US_ADMINISTRATIVE_RULES/parsed/parquet/state_admin_rules_cid/README.md

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+# US State Administrative Rules (CID-Keyed Parquet)
+
+This folder contains a multi-state administrative-rules dataset exported as Parquet and indexed by IPFS content ID (`ipfs_cid`).
+
+## Snapshot
+- Generated from canonical cleaned run: `canonical_merged_20260310_220852_cleaned_20260310_221150`
+- States covered: 50
+- Combined source rows: 1589
+- Combined unique CIDs: 1589
+- Source parquet files: 101 (50 per-state + 1 combined)
+- Embeddings parquet files: 51 (50 per-state + 1 combined)
+- Embedding model: `thenlper/gte-small`
+- Embedding provider runtime: `embeddings_router` (`local_adapter`)
+
+## Source Parquet Schema
+Primary key column (CID-first ordering):
+- `ipfs_cid`
+- `state_code`
+- `source_id`
+- `identifier`
+- `name`
+- `legislation_type`
+- `legislation_jurisdiction`
+- `source_url`
+- `text`
+- `jsonld`
+
+## Embeddings Parquet Schema
+Primary key column (CID-first ordering):
+- `ipfs_cid`
+- `state_code`
+- `semantic_text`
+- `embedding_model`
+- `embedding`
+
+Semantic embedding input was restricted to semantic text columns:
+- `name`
+- `text`
+
+## Manifests
+- `manifest.parquet.json`: source conversion stats and per-state row counts
+- `embeddings_manifest.json`: embeddings build stats and per-file summaries
+
+## Quick Query Examples
+### DuckDB: inspect source rows
+```sql
+SELECT state_code, identifier, name
+FROM read_parquet('state_admin_rules_all_states.parquet')
+WHERE ipfs_cid IS NOT NULL
+LIMIT 20;
+```
+
+### DuckDB: join source with embeddings on CID
+```sql
+SELECT s.state_code, s.identifier, s.name, e.embedding_model
+FROM read_parquet('state_admin_rules_all_states.parquet') s
+JOIN read_parquet('state_admin_rules_all_states_embeddings.parquet') e
+  ON s.ipfs_cid = e.ipfs_cid
+LIMIT 20;
+```
+
+### Python: load one state
+```python
+import pyarrow.parquet as pq
+
+table = pq.read_table('STATE-CA.parquet')
+print(table.num_rows, table.column_names)
+```