fix(packaging): move templates/ into decnet/ package so they ship with pip install

The docker build contexts and syslog_bridge.py lived at repo root, which
meant setuptools (include = ["decnet*"]) never shipped them. Agents
installed via `pip install $RELEASE_DIR` got site-packages/decnet/** but no
templates/, so every deploy blew up in deployer._sync_logging_helper with
FileNotFoundError on templates/syslog_bridge.py.

Move templates/ -> decnet/templates/ and declare it as setuptools
package-data. Path resolutions in services/*.py and engine/deployer.py drop
one .parent since templates now lives beside the code. Test fixtures,
bandit exclude path, and coverage omit glob updated to match.

decnet/engine/deployer.py

@@ -31,7 +31,7 @@ from decnet.network import (
 log = get_logger("engine")
 console = Console()
 COMPOSE_FILE = Path("decnet-compose.yml")
-_CANONICAL_LOGGING = Path(__file__).parent.parent.parent / "templates" / "syslog_bridge.py"
+_CANONICAL_LOGGING = Path(__file__).parent.parent / "templates" / "syslog_bridge.py"
 
 
 def _sync_logging_helper(config: DecnetConfig) -> None: