docs: make the service map the front door of architecture.md

The Layering ASCII diagram was cluttered, lumped THE concrete loop plugin
undifferentiated into a grab-bag plugins box, omitted dsh-agent-core and the
app packages, and restated the dependency rule that packages/README.md
already owns — while being the first thing a reader linked from README hits.

- Drop the Layering section; the tier story becomes one intro sentence and
  the dependency rule a one-line Service map footer linking
  packages/README.md#dependencies.
- Split the Service map into the spine (packages/core/) vs the swappable
  capability seams; annotate ctx.agentLoop as THE concrete loop plugin.
- Promote Cordis waterfall semantics to a top-level section placed before
  first waterfall use; drop '(important)' from the heading (anchor swept:
  AGENTS.md, gen-cordis-catalog.ts + regenerated catalog).
- Promote Event taxonomy to a top-level section (anchor unchanged).
- Retitle 'The vocabulary (dsh-llm)' to 'Content blocks and streaming
  (dsh-llm)' so the heading names its content (citation swept:
  llm-streaming.md).

Net -29 words (1851 -> 1822); the 1890 ceiling stands, keeping the
manifest's working margin.

docs/core-data-structures/llm-streaming.md

@@ -62,7 +62,7 @@ interface TokenUsage {
 
 ## The seam
 
-`LlmAdapter` is the provider seam: subclass, implement `stream()`, register with `ctx.llm.registerAdapter(models, adapter)`. The `block-start` / `block-end` `index` correlation and the assembler together mean an adapter only has to emit well-formed chunks — block reassembly is not each adapter's problem. The consumer surface (`ctx.llm.stream()`) and the `llm/stream` waterfall are described in [architecture.md § The vocabulary](../architecture.md#the-vocabulary-dsh-llm).
+`LlmAdapter` is the provider seam: subclass, implement `stream()`, register with `ctx.llm.registerAdapter(models, adapter)`. The `block-start` / `block-end` `index` correlation and the assembler together mean an adapter only has to emit well-formed chunks — block reassembly is not each adapter's problem. The consumer surface (`ctx.llm.stream()`) and the `llm/stream` waterfall are described in [architecture.md § Content blocks and streaming](../architecture.md#content-blocks-and-streaming-dsh-llm).
 
 `ContentBlockType` (the key set the `index`-correlated blocks carry) derives from `ContentBlockMap`: