cmds.secrets.CompileTemplates: Fix conf line handling

File attributes of the compiled output of "jw-pkg secrets
compile-templates" can be specified via the # conf line atop a .jw-tmpl
file, the parsing of that line is buggy, however.

Its mode is parsed as a decimal number unless it carries a leading zero, so
"mode=640" yields 640 decimal, 1200 octal, and the output file ends up
without usable permissions.  The same decimal parse applies to a conf line atop
the .jw-secret of a target, whose attributes are honored the same way, and
the --mode option of compile-templates passes its string value through to
Attrs, whose mode is typed int, so a target without a conf line of its own
crashes in _format_metadata().

Other than that, the # conf line itself should be removed from the compiled
output, but isn't.

This commit makes the conf line handling correct:

- _parse_attributes() parses the mode as octal, with or without a leading
  zero
- _compile_one_template_file() drops the conf line from the compiled
  content
- the --mode option is converted to an octal int by octal_mode() at the
  argument boundary

The integration test writes its conf line modes without leading zeros,
expects the conf line gone from the compiled output, takes one target's
mode from a conf line atop its .jw-secret, and passes a --mode that the
conf lines override.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v1.1.0
Signed-off-by: Jan Lindemann <jan@janware.com>

test/integration/jw-pkg/help/test-expected.txt

@@ -846,7 +846,7 @@ options:
   -h, --help         show this help message and exit
   --owner, -o OWNER  Default output file owner (default: None)
   --group, -g GROUP  Default output file group (default: None)
-  --mode, -m MODE    Default output file mode (octal) (default: None)
+  --mode, -m MODE    Default output file mode (default: None)
 ============= Running: jw-pkg.py -t ../../../.. --log-level info secrets install --help
 usage: jw-pkg.py secrets install [-h] [--only-missing] src [packages ...]