sync(chunk 2a): vendor dav4jvm 2.2.1 as :dav

JitPack-only publishing conflicts with FAIL_ON_PROJECT_REPOS, artifacts are
unsigned and not immutable, and upstream shipped two breaking majors 19 days
apart. 2.2.1 is the last OkHttp release: 3.0.0 moved to Ktor and 4.x needs
Java 21, and SYNC.md's whole auth section is written in OkHttp terms, so 4.x
would have invalidated it. A plain JVM module, not an Android library — the
tree has no Android imports and keeping it that way keeps the floret-kit
extraction a file move.

Four changes from upstream, all in dav/PROVENANCE.md:
- commons-lang3 dropped (one import, one call). The replacement requires the
  whole string to be consumed, as DateUtils did: pattern 1 ends in a literal
  'GMT', so SimpleDateFormat would match "...GMT+02:00" as a prefix and throw
  the offset away.
- HTTP dates were parsed and formatted in the device's local zone — the GMT in
  the format string is a quoted literal and timeZone was never set, so every
  getlastmodified was out by the local UTC offset. Upstream tests dates
  nowhere. The formatter is also no longer shared and mutable.
- dav4jvm#209: permanent redirects now reach the caller via
  DavResource.permanentLocation, cleared per request so it never describes an
  earlier one.
- xpp3 is compileOnly; Android supplies org.xmlpull.v1.

SYNC.md's other claimed defect, "does not follow 303", is not true of 2.2.1 —
pinned by a test rather than removed from the notes.

CI names :dav:test explicitly; testDebugUnitTest is Android-only and would
have run none of the vendored suite. lintDebug added to the per-chunk checks
after it caught a literal byte-order mark left by chunk 1.

settings.gradle.kts

@@ -26,4 +26,5 @@ dependencyResolutionManagement {
 
 rootProject.name = "Agendula"
 include(":app")
+include(":dav")
 includeBuild("floret-kit")