Python SDK: typed local client and lifecycle API

[SarthakWade]

Scope

Publish a Python SDK generated from or validated against the canonical SDK schema.

Provide synchronous and asynchronous clients for host lifecycle, sessions, navigation, semantic inspection, interactions, waits, capture, diagnostics, capabilities, typed errors, cancellation, and timeouts. It should use the existing local transport and require no network service.

Constraints

• Do not maintain handwritten protocol definitions separate from the canonical schema.
• Preserve untrusted-content markings in public result types.
• Credential operations use aliases and challenge IDs only.
• Subprocess cleanup must work after cancellation, exceptions, signals, and interpreter shutdown.
• Unsupported capabilities fail explicitly.

Acceptance criteria

• Supported Python versions and operating systems are documented.
• Formatting, static typing, packaging, unit tests, and integration tests pass.
• Golden fixtures prove parity with the Swift protocol and TypeScript SDK.
• Tests cover startup failure, timeout, cancellation, malformed response, protocol mismatch, and cleanup.
• Source distributions and wheels contain only intended files and include provenance and compatibility metadata.
• Examples demonstrate both synchronous and asynchronous usage.

Blocked by #163.

[yashranaway]

Blocked on #163. Same as the TypeScript SDK: wait for the schema, then generate.