style: apply formatting fixes before linter setup

[nearlyforget]

Description
This PR applies consistent code style and structural fixes across the
repository. These changes were automatically generated by pre-commit
hooks (Ruff, Prettier, and standard file-hygiene tools).

Note: This PR contains zero functional changes. It is intended to be
merged first to "clean the slate" so that future feature PRs are not
cluttered with unrelated formatting diffs.

Key Changes

• Python (Ruff): Standardized indentation, import sorting, and linting
  fixes across all Python samples (a2a/business_agent, rest/python).
• TypeScript/Frontend (Prettier): Unified formatting for React
  components, Node.js scripts, and TypeScript configurations
  (a2a/chat-client, rest/nodejs).
• Markdown & Documentation: Fixed inconsistent spacing, list
  formatting, and table structures in all .md files.
• Data Integrity: Validated and formatted JSON/CSV test data files to
  ensure they are well-formed and end with proper newlines.
• Hygiene: Removed trailing whitespace and fixed missing end-of-file
  newlines across 70+ files.