list_sessions_from_store exposes invalid session IDs returned by adapters

### Summary

Store-backed session listing does not validate session IDs, unlike filesystem listing and individual store-backed lookup.

### Affected code

- `src/claude_agent_sdk/_internal/sessions.py:1525-1575`
- `src/claude_agent_sdk/_internal/sessions.py:1637-1685`
- `src/claude_agent_sdk/_internal/sessions.py:1723-1732`
- `src/claude_agent_sdk/_internal/session_summary.py:219-222`

### Current behavior

The slow path passes every `session_id` returned by `SessionStore.list_sessions()` into loads and then into `SDKSessionInfo`. The fast path similarly copies IDs from session summaries or listings into slots without `_validate_uuid()`.

By contrast:

- filesystem listing skips filenames that are not UUIDs;
- `get_session_info_from_store()` returns `None` for an invalid UUID;
- mutation helpers reject invalid IDs.

### Why this matters

A malformed, stale, or externally populated backend row becomes a public `SDKSessionInfo` and consumes an offset/limit position. The SDK can therefore return session IDs that its own get, resume, fork, and mutation APIs reject.

It also causes inconsistent behavior between otherwise equivalent disk, slow-store, and summary-fast listing paths.

### Expected behavior

All public session listing implementations should filter invalid session IDs before loading, sorting, or pagination.

### Possible fix

Validate IDs as soon as adapter results are received:

- filter `list_sessions()` entries before scheduling loads;
- filter summary entries before conversion;
- ensure malformed entries do not consume page positions.

Add conformance tests for invalid UUIDs in both optional listing methods and verify parity between fast and slow paths.

### Environment

- Repository revision: current `main` audit at SDK version 0.2.128
- Bundled CLI version: 2.1.220
- Python test suite: 1,291 passed, 5 skipped
- Ruff and mypy: clean

I searched the existing issues and pull requests using the affected symbols and behavior before filing this.

Read the affected listing paths in src/claude_agent_sdk/_internal/sessions.py and the summary conversion in src/claude_agent_sdk/_internal/session_summary.py, following _validate_uuid() and SessionStore.list_sessions(). Add conformance tests covering invalid UUIDs in both optional listing methods, then verify fast and slow paths filter malformed entries before loading, sorting, or pagination.

Written by the indexing model from the issue text.