docs!: Audit and document the v1 public API

[marandaneto]

💡 Motivation and Context

Issue #207 needs an upgrade guide, current v1 documentation, and an explicit review of the public API before it becomes stable.

This adds a 0.x to 1.0 migration guide covering the removed capture feature and V0 path, capture result changes, removed feature flag methods, secret_key, and response type renames. It removes stale V0 wording from current API documentation.

The public API audit makes server response types non-exhaustive before 1.0 so minor releases can represent new backend fields and variants. LocalEvaluationResponse::new preserves a supported way to create offline definitions. The generated snapshot records these API stability decisions.

The final package-name snapshot review remains gated on #183, and TLS remains gated on the unresolved work from #201.

Part of #207.

💚 How did you test it?

• cargo fmt --all -- --check
• scripts/check-public-api.sh
• cargo check --examples
• cargo test --workspace
• cargo test --no-default-features
• Autoreview passed on 5263925

📝 Checklist

• I reviewed the submitted code.
• I added or updated tests to verify the changes.
• I updated the docs.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

[greptile-apps]

Prompt To Fix All With AI

### Issue 1
docs/migration-0.x-to-1.0.md:43
**Durability check accepts unsent events**

When a client is disabled or `before_send` filters the entire batch, `all_persisted()` returns true despite no events being submitted, so following this guidance can advance durable state without delivering the intended events. Callers must also verify that `submitted()` equals the intended event count.

```suggestion
`CaptureSummary::not_persisted()` and `CaptureSummary::all_persisted()` now use those per-event results. In the V0 path they reported a successful `2xx` as fully persisted without per-event confirmation. Applications that advance durable state after `capture_immediate` should check both that `submitted()` equals the number of intended events and that `all_persisted()` is true, because disabled clients and fully `before_send`-filtered batches submit no events but still report `all_persisted()` as true.
```

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "docs!: audit and document the v1 public ..." | Re-trigger Greptile}