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>

startos/manifest/index.ts

@@ -14,7 +14,7 @@ export const manifest = setupManifest({
   volumes: ['main'],
   images: {
     spaces: {
-      source: { dockerTag: 'horologger/spaces:v0.2.1' },
+      source: { dockerTag: 'horologger/spaces:v0.2.1a' },
       arch: ['x86_64', 'aarch64'],
     },
     subspaces: {

startos/versions/current.ts

@@ -3,7 +3,7 @@ import { IMPOSSIBLE, VersionInfo } from '@start9labs/start-sdk'
 export const current = VersionInfo.of({
   version: '0.2.1:3',
   releaseNotes: {
-    en_US: `Packaging-only revision — no upstream image changes (\`spaces:v0.2.1\`, \`subs:v0.1.2\`, \`certrelay:v0.2.5\`, \`nacho:v1.0.0\`).
+    en_US: `**Spaces image** pinned to \`horologger/spaces:v0.2.1a\` (other images unchanged: \`subs:v0.1.2\`, \`certrelay:v0.2.5\`, \`nacho:v1.0.0\`).
 
 **Fix:** the Space-CLI web terminal no longer runs \`monitor\` on every login. The MOTD heredoc in \`.bashrc\` now uses a quoted delimiter so backticks in the banner (e.g. around \`monitor\`) are printed literally instead of executing command substitution.