Add documentation and runnable examples

[jaredjakacky]

Summary

Add the documentation and runnable examples for dependkit.

Included in this batch

• expanded project README
• getting-started guide
• usage guide
• lifecycle and readiness guide
• observability guide
• advanced composition guide
• public API map
• examples guide and directory index
• ten runnable examples progressing from the core registry to full Kit Series
  composition

Why this batch now

The core registry and optional adapters are in place. This batch documents the
public surface and adds runnable examples that show the intended adoption path.

The examples begin with the framework-neutral registry and build outward into
readiness policy, stale state, sanitization, structured logs, OpenTelemetry,
Servekit, Workerkit, and full production-style composition.

Notes

• examples use deterministic local checks and noop telemetry providers where
  appropriate
• the root package remains usable without Servekit, Workerkit, or OpenTelemetry
  adapters
• the full package validation workflow is intentionally deferred until the next
  batch

Verification

• make fmt-check
• make vet
• make test
• make test-race
• make build-examples

Follow-up

The next batch will restore the full package validation workflow.