Play Framework

revert: drop playDeps task — Gradle handles dependency resolution natively (PF-90)

The previous two commits (9915e038e, 5e24f1398) added playDeps as a
"compatibility task" mirroring python `play deps --sync`. On reflection
that's exactly the kind of python-era ceremony 1.13.0 is supposed to
shed.

Why playDeps adds nothing:
- All play1 tasks (playRun, playStart, playPrecompile, playAutotest,
  playJavadoc, playBundle, playClasspath, playEvolutions, etc.) pull
  dependencies from sourceSets.main.runtimeClasspath, which Gradle
  resolves on demand the first time any task needs them.
- lib/ doesn't need to be populated for any plugin-driven workflow.
- For Docker / deployment, playBundle already produces a self-contained
  zip with all jars embedded — no separate resolve+materialize step.

Migration of existing python-era Dockerfiles:
- old: `RUN play deps --sync && play precompile && play start`
- new: `RUN gradle playBundle` then unzip and `bash bin/play-start.sh`
  (per the Dockerfile pattern in 8a65578e7's commit message).

Existing scripts that still call `gradle playDeps` will fail with
"task not found" — which is the right signal to update them, not to
silently work via a no-op compatibility shim.

Plugin task count back to 22 (was briefly 23 with playDeps).