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/main.py

@@ -11,11 +11,12 @@ from pathlib import Path
 from .commands import issue_group
 from .backend_commands import backend_group
 from .sync_commands import sync_group
+from .serve_command import serve_command
 from .. import __version__
 
 
 @click.group()
-@click.version_option(version=__version__, package_name='issue-tracker')
+@click.version_option(version=__version__, package_name='issue-core')
 @click.option('--config', type=click.Path(), help='Configuration file path')
 @click.option('--backend', help='Backend to use (local, gitea)')
 @click.option('--verbose', '-v', is_flag=True, help='Verbose output')
@@ -52,6 +53,7 @@ def cli(ctx, config, backend, verbose):
 cli.add_command(issue_group, name='issue')
 cli.add_command(backend_group, name='backend')
 cli.add_command(sync_group, name='sync')
+cli.add_command(serve_command)
 
 
 # Convenience aliases - direct issue commands