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.

pyproject.toml

@@ -93,7 +93,7 @@ filterwarnings = [
 
 [tool.coverage.run]
 source = ["decnet"]
-omit = ["*/tests/*", "templates/*"]
+omit = ["*/tests/*", "*/templates/*"]
 parallel = true
 
 [tool.coverage.report]
@@ -105,7 +105,12 @@ skip_covered = false
 where = ["."]
 include = ["decnet*"]
 
+[tool.setuptools.package-data]
+# Ship docker build contexts + syslog_bridge.py as package data so they land
+# in site-packages when agents install the bundle via `pip install`.
+decnet = ["templates/**/*"]
+
 [tool.bandit]
 exclude_dirs = [
-    "templates/syslog_bridge.py",
+    "decnet/templates/syslog_bridge.py",
 ]