new: add pkh put, a native dput replacement for PPA uploads

Upload built source packages over SFTP with host-key verification
(Launchpad fingerprints pinned in host_keys.yml, ask-to-accept
otherwise), Launchpad account discovery (git config lp.user), and
pre-flight checks the upload queue itself never does: changes file
discovery/validation, PPA existence via the Launchpad API, target
series validity, and debian/control Section validity (sections
bundled in distro_info.yml). Upload log prevents duplicate uploads
unless --force.

README.md

@@ -29,6 +29,7 @@ Commands:
   chlog  Auto-generate changelog entry, editing it, committing it afterwards
   build  Build the source package (into a .dsc)
   deb    Build the source package into binary package (.deb)
+  put    Upload the built source package to a PPA
   help   Print this message or the help of the given subcommand(s)
 ```
 
@@ -104,7 +105,7 @@ Missing features:
 - [ ] `pkh status`
   - [ ] Show build status
 - [ ] `pkh put`
-  - [ ] Upload the source package to a PPA
+  - [x] Upload the source package to a PPA (native SFTP, no `dput` dependency)
   - [ ] Upload the source package to the archive
 - [ ] `pkh commit`
   - [ ] Commit the changes to git