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/versions/v1.0.0.0.ts

@@ -8,7 +8,7 @@ export const v_1_0_0_0 = VersionInfo.of({
 - Depends on the Spaces service and auto-connects to its spaced JSON-RPC at spaces.startos:7225 by reading the Spaces RPC credentials from the mounted Spaces volume.
 - Generates a Nostr operator keypair and a strong session secret on first install. "Show Operator Credentials" and "Import Operator Key" actions manage the keypair.
 - "Show Admin Credentials" surfaces the fixed, well-known admin login baked into the image, with a warning to keep the service private.
-- "Configure Platform" optionally sets the Nostr relay, theme mode, CoinGecko pricing, and SUBSD backend.`,
+- "Configure Platform" optionally sets the Nostr relay, theme mode, CoinGecko pricing, and SUBS backend.`,
   },
   migrations: {
     up: async ({ effects }) => {},