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>

issue_core/cli/serve_command.py

@@ -0,0 +1,43 @@
+"""
+`issue serve` — launch the issue-core REST API.
+
+Requires the [api] extra: `pip install issue-core[api]`.
+"""
+
+import click
+
+
+@click.command("serve")
+@click.option("--host", default="127.0.0.1", show_default=True, help="Bind address.")
+@click.option("--port", default=8765, show_default=True, type=int, help="Bind port.")
+@click.option("--reload", is_flag=True, default=False, help="Auto-reload on code change (dev only).")
+@click.option("--log-level", default="info", show_default=True, help="Uvicorn log level.")
+def serve_command(host: str, port: int, reload: bool, log_level: str) -> None:
+    """Launch the issue-core REST API (POST /issues/ ingestion endpoint).
+
+    Requires ISSUE_CORE_API_KEY to be set in the environment.
+    """
+    try:
+        import uvicorn  # noqa: F401
+    except ImportError:
+        raise click.ClickException(
+            "The 'api' extra is not installed. Run: pip install 'issue-core[api]'"
+        )
+
+    from ..api.auth import AuthConfigError, get_configured_api_key
+
+    try:
+        get_configured_api_key()
+    except AuthConfigError as exc:
+        raise click.ClickException(str(exc))
+
+    import uvicorn
+
+    uvicorn.run(
+        "issue_core.api.app:create_app",
+        host=host,
+        port=port,
+        reload=reload,
+        log_level=log_level,
+        factory=True,
+    )