Rename SUBSD_* env vars to SUBS_* to match upstream refactor

The upstream SpacesOps app refactored its SUBSD_* environment variables to
SUBS_* (verified against server.js in spacesops/spacesops:v1.0.0). Update the
package to match so the configured values reach the app:

- main.ts: inject SUBS_URI_VALUE / SUBS_RPC_USER / SUBS_RPC_PASSWORD.
- configurePlatform action + storeJson: rename store keys subsd*→subs* and the
  field labels/descriptions (SUBS URL / SUBS RPC User / SUBS RPC Password).
- README, instructions, release notes: SUBSD→SUBS.

Note: the image's /app/setup-spacesops-env.sh still exports SUBSD_* defaults
(partial upstream refactor) — see report; vars the package does not set (e.g.
SUBS_RPC_URL) currently have no in-image default.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

startos/main.ts

@@ -102,9 +102,9 @@ export const main = sdk.setupMain(async ({ effects }) => {
   if (store.coingeckoApiKey) env.COINGECKO_API_KEY = store.coingeckoApiKey
   if (store.coingeckoTokenCoins)
     env.COINGECKO_TOKEN_COINS = store.coingeckoTokenCoins
-  if (store.subsdUrl) env.SUBSD_URI_VALUE = store.subsdUrl
-  if (store.subsdUser) env.SUBSD_RPC_USER = store.subsdUser
-  if (store.subsdPassword) env.SUBSD_RPC_PASSWORD = store.subsdPassword
+  if (store.subsUrl) env.SUBS_URI_VALUE = store.subsUrl
+  if (store.subsUser) env.SUBS_RPC_USER = store.subsUser
+  if (store.subsPassword) env.SUBS_RPC_PASSWORD = store.subsPassword
 
   return sdk.Daemons.of(effects).addDaemon('spacesops', {
     subcontainer: sub,