docs: fix go.work claim in AGENTS.md (#30)

* docs: remove stale cmd/eyrie/ doc references

The eyrie/docs/ARCHITECTURE.md Components diagram and the README.md
build instructions both referenced a cmd/eyrie/ directory that does
not exist — eyrie is a library, not a CLI. Reword the docs to
reflect the library-only reality:

- docs/ARCHITECTURE.md: drop the 'cmd/eyrie/' tree entry, keep the
  api/openapi.yaml entry (the OpenAPI spec documents the embedded
  HTTP server in internal/api, not a standalone binary).
- README.md: replace 'go build ./cmd/eyrie' with 'go build ./...'
  to match Makefile:46 (the build target is just 'go build ./...'
  to verify the library compiles).

* docs: fix go.work claim in AGENTS.md

The previous text said 'go.work points at hawk's external/ for local dev', but
eyrie/go.work only contains:

  go 1.26.4
  use .
  replace github.com/GrayCodeAI/tok => ../tok

It does NOT have a hawk/external/eyrie replace. That replace lives in hawk/go.work
(see hawk-eco/hawk/.gitmodules and the checkout-eyrie composite action). Update the
comment to reflect reality and warn that adding other replaces here would conflict
with hawk's workspace.

Author: Patel230

AGENTS.md

@@ -46,7 +46,7 @@ make ci                          # Full CI suite
 
 - Provider interface is the boundary — keep it stable
 - Streaming tests need careful goroutine management
-- `go.work` points at hawk's `external/` for local dev
+- `go.work` here replaces only `github.com/GrayCodeAI/tok => ../tok`; hawk's own `go.work` adds an `external/eyrie` replace so hawk can develop against a local eyrie checkout. Do not add other `replace` directives here without coordinating with hawk's workspace.
 
 ## Naming Conventions