docs: add pages for telemetry and the runtime modules, plus a source-to-sink quickstart

[joshua-temple]

What this change does

Adds documentation-site coverage for the modules that had none, and surfaces the runtime modules that were previously kept out of the public README:

• New overview pages for telemetry (+ a slog/otel/datadog adapters page), durable, cluster, transport, and wasm.
• A source -> state -> sink quickstart (start/ingest-drive-emit.md): consume an event, drive a machine, emit an effect.
• Sidebar (astro.config.mjs): a Telemetry group and a Runtimes group (Durable/Cluster/Transport/WASM), via autogenerate.
• README Modules table: honest experimental rows for durable/cluster/transport/wasm (the broker "planned" row stays).

Every code snippet was checked against the real exported signatures (cluster.NewSystem/Capture/Restore, durable.NewRunner/Recover/StateAt, transport.DurableTimeTravel/StateAt, wasm.Compile/Guard, state.MarshalSnapshot/UnmarshalSnapshot, statemachine.Drive/NewMemStore, sink.NewManifold/WithOutlets). source/cdc was already documented in codecs.md. Hero images are tracked IMAGE-SLOT placeholders, not live tags, so nothing references a missing asset. Verified with a full npm run build (80 pages, no errors or broken-link warnings).

Why

Four shipped modules were invisible to the docs site and absent from the README, and there was no quickstart spanning the IO seams. This makes the surface honest and navigable for the 1.0 cut.

Checklist

• Commits signed off (DCO) and conventional
• Snippets verified against real APIs; npm run build clean