feat: add fast-apply, model-router, and open-source-models examples

Half the docs nav had no examples at all. Each new directory has a README and
runnable TypeScript (plus Python where a second language earns its keep).

- fast-apply/: basic-apply, streaming-apply (reports measured tok/s), and
  agent-loop — Claude emits a lazy `// ... existing code ...` snippet and
  morph-v3-fast merges it to disk, which is the pattern people actually ship.
- model-router/: classify shows difficulty/ambiguity/domain diverging across
  contrasting prompts; multimodel runs one input under all four policies so you
  can see the pick change, then calls the model it routed to.
- open-source-models/: basic-chat, streaming, and tools-and-json. Catalog table
  is generated from morphllm.com/api/models/json rather than hand-written.

All model IDs verified against the live catalog; every example was run against
the API before commit.