feat: Implement boto3-compatible dict responses (Phase 2)

Changed list_objects() to return boto3-compatible dict instead of custom
ListObjectsResponse dataclass. This makes DeltaGlider a true drop-in replacement
for boto3.client('s3').

Changes:
- list_objects() now returns dict[str, Any] with boto3-compatible structure:
  * Contents: list[S3Object] (dict with Key, Size, LastModified, etc.)
  * CommonPrefixes: list[dict] for folder simulation
  * IsTruncated, NextContinuationToken for pagination
  * DeltaGlider metadata stored in standard Metadata field

- Updated all client methods that use list_objects() to work with dict responses:
  * find_similar_files()
  * get_bucket_stats()
  * CLI ls command

- Updated all tests to use dict access (response['Contents']) instead of
  dataclass access (response.contents)

- Updated examples/boto3_compatible_types.py to demonstrate usage

- DeltaGlider-specific metadata now in Metadata field:
  * deltaglider-is-delta: "true"/"false"
  * deltaglider-original-size: string number
  * deltaglider-compression-ratio: string number or "unknown"
  * deltaglider-reference-key: optional string

Benefits:
- True drop-in replacement for boto3
- No learning curve - if you know boto3, you know DeltaGlider
- Works with any boto3-compatible library
- Type safety through TypedDict (no boto3 import needed)
- Zero runtime overhead (TypedDict compiles to plain dict)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/boto3_compatible_types.py

@@ -1,7 +1,11 @@
-"""Example: Using boto3-compatible types without importing boto3.
+"""Example: Using boto3-compatible responses without importing boto3.
 
-This demonstrates how DeltaGlider provides full type safety without
-requiring boto3 imports in user code.
+This demonstrates how DeltaGlider provides full type safety and boto3 compatibility
+without requiring boto3 imports in user code.
+
+As of v5.0.0, DeltaGlider returns plain dicts (not custom dataclasses) that are
+100% compatible with boto3 S3 responses. You get IDE autocomplete through TypedDict
+type hints without any runtime overhead.
 """
 
 from deltaglider import ListObjectsV2Response, S3Object, create_client
@@ -17,6 +21,7 @@ def process_files(bucket: str, prefix: str) -> None:
         Bucket=bucket, Prefix=prefix, Delimiter="/"
     )
 
+    # Response is a plain dict - 100% boto3-compatible
     # TypedDict provides autocomplete and type checking
     for obj in response["Contents"]:
         # obj is typed as S3Object - all fields have autocomplete!
@@ -24,6 +29,12 @@ def process_files(bucket: str, prefix: str) -> None:
         size: int = obj["Size"]  # ✅ IDE knows this is int
         print(f"{key}: {size} bytes")
 
+        # DeltaGlider metadata is in the standard Metadata field
+        metadata = obj.get("Metadata", {})
+        if metadata.get("deltaglider-is-delta") == "true":
+            compression = metadata.get("deltaglider-compression-ratio", "unknown")
+            print(f"  └─ Delta file (compression: {compression})")
+
     # Optional fields work too
     for prefix_dict in response.get("CommonPrefixes", []):
         print(f"Directory: {prefix_dict['Prefix']}")
@@ -49,3 +60,5 @@ if __name__ == "__main__":
     print("✅ Full type safety without boto3 imports!")
     print("✅ 100% compatible with boto3")
     print("✅ Drop-in replacement")
+    print("✅ Plain dict responses (not custom dataclasses)")
+    print("✅ DeltaGlider metadata in standard Metadata field")