update logos, favicon and brand names

[GSemikozov]

No description provided.

[linear]

PYD-2115 Migrate brand for all websites and repos

[hyperlint-ai]

PR Change Summary

Updated branding elements across documentation to reflect the new name 'Pydantic AI' and improved references to 'Pydantic Validation'.

• Changed all instances of 'PydanticAI' to 'Pydantic AI' for consistency.
• Updated references from 'Pydantic' to 'Pydantic Validation' where applicable.
• Modified the README and other documentation files to reflect the new branding.

Modified Files

• README.md
• docs/agents.md
• docs/index.md
• docs/logfire.md
• examples/README.md
• pydantic_ai_slim/README.md
• pydantic_evals/README.md
• pydantic_graph/README.md

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