feat: rename to issue-core and add task ingestion endpoint

Renames the package, distribution, CLI alias, Makefile targets, and
working directory from issue-facade to issue-core, signalling its
role as the authoritative task lifecycle manager for the Coulomb org
(peer to activity-core, rules-core, project-core).

Adds POST /issues/ ingestion endpoint for activity-core's IssueSink,
under a new optional [api] extra. The endpoint is served by `issue
serve`, authenticates via the ISSUE_CORE_API_KEY env var (Bearer or
X-API-Key header), and routes the TaskSpec payload to the configured
default backend with full traceability metadata embedded in
sync_metadata.

- T01: Python package issue_tracker -> issue_core, dir rename
- T02: registered in state hub under custodian domain
- T03: INTENT.md (what it is, what it isn't, how it fits)
- T04: SCOPE.md (in/out-of-scope, integration boundaries)
- T05: POST /issues/ via FastAPI + Uvicorn, 9 unit tests
- T06: docs/nats-task-ingestion.md design stub

Closes ISSC-WP-0001.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

feedback/README.md

@@ -65,10 +65,10 @@ If you're integrating this capability into a master project:
 
 ```bash
 cd my-master-project
-echo "Feedback about issue-facade..." > feedback.md
+echo "Feedback about issue-core..." > feedback.md
 
 # Copy to capability's feedback directory
-cp feedback.md capabilities/issue-facade/feedback/inbound/$(date +%Y%m%d-%H%M%S)-sync-issue.md
+cp feedback.md capabilities/issue-core/feedback/inbound/$(date +%Y%m%d-%H%M%S)-sync-issue.md
 ```
 
 ### What to Include
@@ -140,7 +140,7 @@ mv feedback/inbound/20251217-feature-request.md feedback/reviewed/
 Each capability maintains its own feedback directory. Users navigate to the capability and submit feedback.
 
 ```bash
-cd capabilities/issue-facade
+cd capabilities/issue-core
 echo "Feedback..." > feedback/inbound/$(date +%Y%m%d)-feedback.md
 ```