Add Debian BTS source for bugs filed and owned

New `bts` subcommand backed by python-debianbts (bugs.debian.org SOAP):

- Identify by email address: get_bugs(submitter=...) for bugs filed,
  get_bugs(owner=...) for bugs owned
- Filed filtered on creation date, owned on log_modified; status
  lookups capped at 500 bugs per collect
- Per-query failures degrade to warnings like other sources

uv.lock

@@ -360,6 +360,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/10/bd/c038d7cc38edc1aa5bf91ab8068b63d4308c66c4c8bb3cbba7dfbc049f9c/pyparsing-3.3.2-py3-none-any.whl", hash = "sha256:850ba148bd908d7e2411587e247a1e4f0327839c40e2e5e6d05a007ecc69911d", size = 122781, upload-time = "2026-01-21T03:57:55.912Z" },
 ]
 
+[[package]]
+name = "python-debianbts"
+version = "4.1.1"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/b5/2c/10993f887ddf762d46540946e4dca6ccf03b9d1799101622b22379670ca4/python_debianbts-4.1.1.tar.gz", hash = "sha256:f443b18ce2411b373103784715e6707df034f48dad7be387a6917b16e154d793", size = 16585, upload-time = "2024-06-09T07:42:15.973Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/fd/7c/b1dfbaa44e8a4a992443dbe21d0c37e77b820ff069a9d0eb9df917934dbd/python_debianbts-4.1.1-py3-none-any.whl", hash = "sha256:9900941d94a41039520fc25847bb74cad92eacf14698c9fbd3f4d2360a1c2161", size = 11063, upload-time = "2024-06-09T07:42:13.822Z" },
+]
+
 [[package]]
 name = "pywin32-ctypes"
 version = "0.2.3"
@@ -461,6 +470,7 @@ dependencies = [
     { name = "httpx" },
     { name = "keyring" },
     { name = "launchpadlib" },
+    { name = "python-debianbts" },
 ]
 
 [package.dev-dependencies]
@@ -474,6 +484,7 @@ requires-dist = [
     { name = "httpx", specifier = ">=0.27" },
     { name = "keyring", specifier = ">=25" },
     { name = "launchpadlib", specifier = ">=2.1.0" },
+    { name = "python-debianbts", specifier = ">=4.1.1" },
 ]
 
 [package.metadata.requires-dev]