Refactor: delegate jspod install to jss install (consolidate install plumbing) #48

Now that JSS 0.0.198 ships its own `jss install` subcommand (Phases 1+2+4 of JSS#464), jspod's wrapper-side install is duplicated infrastructure. The two implementations are byte-for-byte similar — both spawn `git clone` + dual-push, both have the same spec parser, both fetch tokens the same way.

Why consolidate

• Single source of truth. Phase 5 (curated default set), Phase 6 (`--bundle`), Phase 3 (`--did` resolution) will all land in JSS first. If jspod's install stays separate, every new install feature requires double-porting.
• Wrapper shrinks ~150 LoC (`runInstall`, `parseAppSpec`, `printInstallHelp`).
• Behavior unchanged for users — `npx jspod install chrome` keeps working exactly the same.

When (not yet)

Hold this until JSS install stabilizes:

• JSS#464 Phase 5 lands (curated default set)
• JSS#464 Phase 6 lands (`--bundle`)
• A release cycle or two passes with the JSS install in the wild

Premature consolidation while JSS install is still evolving means re-doing this refactor each time the JSS-side interface shifts.

Sketch

Replace jspod's `runInstall` (~150 LoC) with a ~10-line delegation:

```js
async function runInstall(rest) {
// Default the --pod to the local jspod port; users can still
// override with --pod. Pass everything else through unchanged.
const args = ['install', ...rest];
if (!rest.includes('--pod')) {
args.push('--pod', http://localhost:${options.port});
}
const jssBin = join(__dirname, 'node_modules', '.bin', 'jss');
const child = spawn(jssBin, args, { stdio: 'inherit' });
await new Promise((resolve) => child.on('exit', (code) => {
process.exit(code || 0);
}));
}
```

Drop `parseAppSpec` and `printInstallHelp` — `jss install --help` is the source of truth.

Update jspod's main `--help` to mention "see `jss install --help` for the install subcommand options" or similar.

Risk

Behavior should be identical. Edge cases to verify:

• Error messages: jspod's branded output (`✓ chrome → ...`) is replaced by jss's (also `✓ chrome → ...` — same shape today). If they ever diverge, the wrapper inherits whatever JSS does — that's the point.
• `jspod`-specific defaults (e.g. default pod URL = 5444) get baked in through the `--pod` injection above.

Sibling

• nosdav-server has the same situation; tracked separately on that repo.