Move documents to docs/ and the example config to configs/ (closes #411)

ARCHITECTURE.md and TODO.md move to docs/, config.example.yml to
configs/, as REPO_POLICIES.md asks of the root. Links, the
no-snapshots error message and the example-config test follow them.

Model: opus-5-5

README.md

@@ -599,7 +599,7 @@ both are set.
 
 For an implementation-level view of the internals — the data model, the `fx`
 dependency-injection wiring, and the scanner — see
-[`ARCHITECTURE.md`](ARCHITECTURE.md).
+[`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md).
 
 ### remote storage layout
 
@@ -718,8 +718,8 @@ format does and does not protect.
 ## configuration reference
 
 Run `vaultik config init` to generate a fully commented config file; a complete
-annotated example also lives in [`config.example.yml`](config.example.yml). Key
-fields:
+annotated example also lives in
+[`configs/config.example.yml`](configs/config.example.yml). Key fields:
 
 | Field                | Default                         | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
 | -------------------- | ------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |