Pin spaces image to v0.2.1a and align docs

The manifest now bundles horologger/spaces:v0.2.1a; README, instructions,
and 0.2.1:3 release notes match so pack and user-facing text stay in sync.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -37,7 +37,7 @@ through a browser-based terminal.
 
 | Field | Value |
 | --- | --- |
-| Spaces image | `docker.io/horologger/spaces` |
+| Spaces image | `docker.io/horologger/spaces:v0.2.1a` |
 | Subspaces image | `docker.io/horologger/subs:v0.1.2` |
 | Certrelay image | `docker.io/horologger/certrelay:v0.2.5` |
 | Nacho image | `docker.io/horologger/nacho:v1.0.0` |
@@ -250,7 +250,7 @@ spaces balance
 package_id: spaces
 upstream_version: subspacesplus
 images:
-  spaces: docker.io/horologger/spaces:v0.2.1
+  spaces: docker.io/horologger/spaces:v0.2.1a
   subspaces: docker.io/horologger/subs:v0.1.2
   certrelay: docker.io/horologger/certrelay:v0.2.5
   nacho: docker.io/horologger/nacho:v1.0.0
@@ -285,6 +285,8 @@ spaced_env_vars:
   - BTC_RPC_PASSWORD
   - APP_USER
   - APP_PASSWORD
+spaces:
+  image: horologger/spaces:v0.2.1a   # spaced, space-cli, gotty (terminal image)
 subspaces:
   default_enabled: false   # opt-in via Enable Subspaces action
   store_field: enableSubspaces