feat(core-realtime): scaffold realtime optional core

Generator-emitted scaffold (pnpm turbo gen core-package realtime) plus
the story-00-precedent coverage repairs (coverage provider devDep,
symbols.ts exclude + tested allowlist mirror) and three minimal tests
covering generator-emitted realtime code the template suite misses.
Squash of 31d85e0 + review-fix cf11b38.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

docs/library-decisions/2026-05-14-zod.md

@@ -5,7 +5,7 @@ tier: core
 decision: approved
 date: 2026-05-14
 deciders: [scaffolded]
-adr: adr-015
+adr: adr-016
 filter-results:
   license: MIT
   types: native
@@ -35,7 +35,7 @@ Active. Regular releases by Colin McDonnell; widely adopted.
 
 ## Filter: boundary-fit
 
-Core package. Zod is the workspace-canonical validation library locked in `core-shared` (ADR-015).
+Core package. Zod is the workspace-canonical validation library locked in `core-shared` (ADR-016).
 
 ## Filter: shadow-check
 
@@ -51,7 +51,7 @@ No advisories at adoption time.
 
 ## Filter: named-consumer
 
-`core-events` uses zod for event-descriptor payload schemas.
+`core-realtime` uses zod for channel descriptor and payload schema validation.
 
 ## Prompt: replaces