Packaging via sbt-native-packager

[Sootopolis]

Depends on

None.

Blocks

• Decline subcommand tree
• ccas serve lifecycle (transitively)

What

Add sbt-native-packager with the JavaAppPackaging plugin. Produce a runnable ccas shell wrapper plus lib jars under target/universal/stage/ (via sbt stage).

Single main entry point class (e.g. ccas.cli.Main) that dispatches on the first argv to either the existing CcasServer boot (ccas serve) or the upcoming subcommand tree (separate issue). Empty implementation for the latter is fine in this issue — it can println("not implemented yet") until the decline subcommand tree lands.

Acceptance

• sbt stage produces target/universal/stage/bin/ccas.
• bin/ccas serve boots the existing CcasServer on 127.0.0.1:8080.
• bin/ccas anything-else exits non-zero with a placeholder message.
• README updated with a "Build" section pointing at sbt stage.

Files

• project/plugins.sbt — add sbt-native-packager.
• build.sbt — enable JavaAppPackaging, set Compile / mainClass.
• new src/main/scala/ccas/cli/Main.scala — argv dispatch.
• README.md — build instructions.

Reference

Tracked under epic #40 (CLI v0). Roadmap: ~/.claude/plans/ultra-sparkling-unicorn.md § "Phase 1, new work #1".

[Sootopolis]

Implemented on wip in fe5a763.

• Added sbt-native-packager (JavaAppPackaging); sbt stage emits two launchers under target/universal/stage/bin/: ccas (CLI primary) and ccas-server (forwarder → ccas.server.CcasServer, for hosted deploys). Compile / discoveredMainClasses pinned to those two so the other ZIOAppDefault apps don't leak launcher scripts.
• New ccas.cli.Main dispatches the first arg: serve → CcasServer.run; anything else prints a placeholder and exits non-zero (subcommand tree lands in CLI subcommand tree via decline #46).
• README gained a Build section.

Verified end-to-end: bin/ccas serve against a local Postgres → /health and /health/ready both 200, clean SIGTERM; bin/ccas <other> and bin/ccas (no args) exit 1.

Leaving open until merged to main.