refactor: reorganize examples to mirror the docs nav

Top-level folders now match the docs.morphllm.com Models nav, so whatever you
found in the docs has the same name here.

- warpgrep/: 17 examples regrouped under agents/ and sandboxes/. Wrote the 5
  READMEs that were missing (search-node-modules, github-search,
  github-streaming, agents/vercel, agents/gemini). Pinned every example to
  morph-warp-grep-v2.1; the tree had three spellings of that model.
- basic-search documented a repo-path argument it ignored — it hardcoded
  repoRoot: "." and always searched its own directory. Now takes the path.
- compaction/ -> compact/, and one-prompt-integraion/ -> integration-prompt/.
  Added basic, query-conditioned, and chat-completions examples, and stripped
  the 8 cells of saved execution output from the websearch notebook.
- reflex/ -> reflexes/, one directory per example, each with the package.json
  and requirements.txt it never had. Nothing in there ran out of the box before.
- Root README was four overlapping tables (by language, by use case, by
  platform, then again by example) covering 3 of 7 directories. Now one index.
- Consolidated the per-directory .gitignores and dropped entries for paths that
  no longer exist.