feat: add usage and web2app resources (#parity)

[pbertsch]

Summary

Adds two new resources to the Python SDK to reach parity with the AWSYS.CO MCP server. Both backend endpoints are API-key reachable, and both are implemented in the SDK's dual sync + async structure.

• usage — client.usage.get() → GET /api/user/stats → UsageStats. Live account consumption (links, clicks, QR codes, API calls, tracked clicks) plus current tier limits and active overage state. Distinct from me.get(), which returns the static profile.
• web2app — client.web2app.consume_session(token) → GET /api/v1/web2app/{token} → Web2AppSession. Single-use deep-link sessions with a 24h TTL; 400/404 are handled by the existing transport error mapping.

New models (Pydantic v2, camelCase aliases)

UsageStats, UsageLimits, UsageOverage, Web2AppSession — all exported from the package surface.

Flexible limit fields: The /api/user/stats handler serializes unlimited caps (-1) as the literal string "unlimited" while finite caps stay integers. Verified against the live backend handler (functions/app/routes/user.js). Those fields (links_per_month, monthly_links, daily_links, monthly_tracked_clicks, qr_codes, folders) are typed Optional[Union[int, str]] to match the actual contract; api_calls_per_month and custom_slugs are always integers.

Other

• Wired into both Client and AsyncClient, mirroring existing resource attachment.
• README: added Usage + Web2App sections and Models-table rows.
• Version bumped 1.1.0 → 1.2.0 (also corrected __version__, which was stale at 1.0.0).

Test plan

• pip install -e ".[dev]" then pytest — 153 passed, 26 skipped (skips are credential-gated integration tests, unchanged).
• New unit tests for both resources, sync + async (MagicMock + AsyncMock, mirroring test_trust_score.py): assert endpoint path, parsed model fields, and an "unlimited" limit value.
• AsyncClient wiring tests extended for usage + web2app.
• No ruff/black config present in repo — no lint step to run.

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