[BUG] Media type handling bugs and missing format support

[opieter-aws]

Steps to Reproduce

Bugs:

• WebP images get wrong MIME type with Anthropic provider. anthropic.py:132 uses mimetypes.types_map.get(f".{content['image']['format']}", "application/octet-stream"). Python's mimetypes module returns "application/octet-stream" for .webp, not "image/webp". WebP images will fail or be misprocessed. TypeScript uses an explicit switch statement that correctly maps webp.

• GuardContent wraps unsupported image formats and missing image type support.bedrock.py:450-451 wraps ALL image formats in guardContent without format validation. TypeScript explicitly checks for png/jpeg only and skips unsupported formats. Additionally, GuardContent type (content.py) only has a "text" field — missing "image" support that TypeScript has. Wrapping unsupported formats will cause Bedrock API errors.

• Video format "3gp" not mapped to "three_gp" for Bedrock API. bedrock.py:647 passes video format as-is. TypeScript maps "3gp" → "three_gp" to match the Bedrock API enum. 3GP videos will be rejected by Bedrock.

Missing format support (non-breaking gaps):

• DocumentFormat missing "json" and "xml" (TypeScript has them)
• ImageFormat missing "jpg" alias for jpeg (TypeScript has it)
• ToolResultContent missing video support (TypeScript has VideoBlock)
• DocumentSource missing { text: string } and { content: [...] } source types (TypeScript has them)

Expected Behavior

1. WebP images should get "image/webp" MIME type
2. GuardContent should only wrap supported image formats (png, jpeg) and support image type
3. "3gp" video format should be mapped to "three_gp"
4. Format types should support json, xml documents; jpg alias; video in tool results; text document sources

Actual Behavior

1. WebP → "application/octet-stream" → Anthropic API error
2. Unsupported image formats wrapped in guardContent → Bedrock API error
3. "3gp" sent as-is → Bedrock API error
4. Missing format types limit what content can be represented

Additional context

This was a finding from an agentic cross-SDK consistency scan between Python and TypeScript SDKs (strands-agents/sdk-typescript#789). The finding has been triaged, but verify that this needs an actual fix.