feat: unified first-run flow — merge wizard + gateway install (IUH-M03)

Collapse `mosaic wizard` and `mosaic gateway install` into a single cohesive
first-run experience. Gateway config and admin bootstrap now run as terminal
stages of `runWizard`, sharing `WizardState` with the framework stages and
eliminating the fragile 10-minute `$XDG_RUNTIME_DIR/mosaic-install-state.json`
session-file bridge.

- Extract `gatewayConfigStage` and `gatewayBootstrapStage` as first-class
  wizard stages with full spec coverage (headless + interactive paths).
- `mosaic gateway install` becomes a thin wrapper that invokes the same
  two stages — the CLI entry point is preserved for operators who only
  need to (re)configure the daemon.
- Honor explicit `--port` override even on resume: when the override
  differs from the saved GATEWAY_PORT, force a config regeneration so
  `.env` and `meta.json` cannot drift.
- Honor `state.hooks.accepted === false` in the finalize stage and in
  `mosaic-link-runtime-assets`: declined hooks are now actually opted-out,
  with a stable `mosaic-managed: true` marker in the template so cleanup
  survives template updates without touching user-owned configs.
- Headless rerun of an already-bootstrapped gateway with no local token
  cache is a successful no-op (no more false-positive install failures).
- `tools/install.sh` calls `mosaic wizard` only — the follow-up
  `mosaic gateway install` auto-launch is removed.

Closes mosaicstack/mosaic-stack#427.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/mosaic/__tests__/integration/full-wizard.test.ts

@@ -49,6 +49,7 @@ describe('Full Wizard (headless)', () => {
       sourceDir: tmpDir,
       prompter,
       configService: createConfigService(tmpDir, tmpDir),
+      skipGateway: true,
     });
 
     const soulPath = join(tmpDir, 'SOUL.md');
@@ -75,6 +76,7 @@ describe('Full Wizard (headless)', () => {
       sourceDir: tmpDir,
       prompter,
       configService: createConfigService(tmpDir, tmpDir),
+      skipGateway: true,
     });
 
     const userPath = join(tmpDir, 'USER.md');
@@ -97,6 +99,7 @@ describe('Full Wizard (headless)', () => {
       sourceDir: tmpDir,
       prompter,
       configService: createConfigService(tmpDir, tmpDir),
+      skipGateway: true,
       cliOverrides: {
         soul: {
           agentName: 'FromCLI',