feat(agent): inject S0 env into launchd/systemd via install CLI (S2)

- launchd writer emits <EnvironmentVariables>; systemd writer emits EnvironmentFile/Environment;
  originConfig zone parameterized (default 'term' preserved for relay callers).
- InstallOptions threaded CLI install -> createCliDeps -> installService seam -> writers, so generated
  units carry BIND_HOST (defaults 127.0.0.1 for tunnel hosts), ALLOWED_ORIGINS, PORT, SHELL_PATH,
  IDLE_TTL, USE_TMUX. systemd rejects control chars in env values.
Verified: agent typecheck+build clean; vitest 166/166 (154 baseline + 12 new).

agent/src/cli/deps.ts

@@ -17,6 +17,7 @@ import { generateIdentity } from '../keys/identity.js'
 import { redeemPairingCode } from '../enroll/pair.js'
 import { runTunnel } from '../transport/runTunnel.js'
 import {
+  buildInstallOptions,
   detectPlatform,
   installService as installServiceUnit,
   uninstallService as uninstallServiceUnit,
@@ -74,7 +75,9 @@ export function createCliDeps(): CliDeps {
       process.once('SIGINT', onSignal)
       return handle.done
     },
-    installService: (cfg) => installServiceUnit(cfg, requirePlatform(), realInstallDeps()),
+    resolveInstallOptions: () => buildInstallOptions(process.env),
+    installService: (cfg, options) =>
+      installServiceUnit(cfg, requirePlatform(), realInstallDeps(), options),
     uninstallService: () => uninstallServiceUnit(requirePlatform(), { runCommand, homedir }),
     print: (line) => {
       process.stdout.write(`${line}\n`)