feat: release Goal Runs SDK 0.6.0

[Si40Code]

What changed

• add client.goals support for listing and reading published Goals, creating Goal Runs, polling terminal results, and run_and_wait
• sync the SDK OpenAPI snapshot and generated models/client to CALL-E Developer API 0.6.0
• align webhook guidance with the current unsigned delivery contract and document that terminal events are emitted only after post-call outcome and requested structured results are finalized
• preserve the SDK 0.2 signed verify/unwrap API as deprecated compatibility behavior
• strengthen contract checks, examples, distribution install smoke tests, and PyPI propagation retries

Why

This publishes the reusable Goal API in the Python SDK and incorporates the backend webhook fix that removed HMAC headers and delays terminal publication until complete outcome materialization. The previous public SDK only exposed Calls and documented a signed webhook contract that the current backend no longer emits.

Developer impact

• new stable package version: calle-ai==0.6.0
• new client.goals surface and generated Goal/GoalRun models
• current webhook receivers should parse the JSON event, deduplicate by CALL-E-Event-Id, and treat the endpoint as an untrusted-input boundary
• existing signed webhook helper methods remain source-compatible but are deprecated

Contract source

• backend canonical commit: 0135d229968f7eabc935d281f79a5811d536e471
• OpenAPI SHA-256: 6c8200cb327d8c125eeed9eb55eeacfbe53cb5dc9044589bb07d07614189786b

Checks

• bash scripts/validate.sh
• 39 pytest tests
• Ruff and mypy
• OpenAPI contract verification
• wheel and sdist build plus Twine checks
• fresh-environment install smoke for wheel and sdist
• git diff --check
• staged/untracked secret and approved E2E-number scan

The production Goal E2E is intentionally run separately after the public package is published.