fix: address final-review polish (docs + comments + test coverage)

- AGENTS.md bind-production code block: shows the slim default state
  (no @repo/core-events / @repo/core-realtime imports, BindProductionContext
  with no generic args) with a comment pointing to the scaffold workflow.
  The previous block showed a fully-wired post-scaffold state without
  signaling that none of those packages exist in main.
- bind-protocols.test.ts: top-of-file comment clarifies what these tests
  actually verify (protocol shapes have required methods) vs what the
  spec text might suggest (full assignability of optional packages'
  interfaces — that's verified by the e2e reconstruction tests, not here).
- core-package-generator.md: drops two stale "Until Phases 3-6 land"
  parentheticals — the phases shipped.
- config.test.ts: extends the choices assertion to cover all 4 names
  (realtime, events, trpc, ui).
- marketing-pages bind-* comments: reverse the inverted optional/required
  language. queue (IJobQueue) is from core-shared and always present;
  bus is the optional one (from @repo/core-events when scaffolded).

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

docs/scaffolding/core-package-generator.md

@@ -24,8 +24,6 @@ The generator emits the package files, updates consuming-app config (e.g. `apps/
 | `trpc` | tRPC server setup | Phase 5 |
 | `ui` | Design-system package | Phase 6 |
 
-(Until Phases 3-6 land, the generator will list an empty choices array and reject any selection.)
-
 ## Verifying an existing project
 
 If your project already has a core-* package and you want to verify the generator's template hasn't drifted from the shipped source, use the byte-identical reconstruction snapshot: