refactor: Replace JBang with javax.tools.JavaCompiler for UDF compilation

[velo]

Summary

• Replace JBang external process with in-process javax.tools.JavaCompiler for compiling Flink UDF .java scripts
• Add Mima (eu.maveniverse.mima) for resolving //JDEPS Maven dependencies (replaces JBang's //DEPS)
• Auto-detect UDF files by class hierarchy (no shebang marker needed)
• Old JBang shebang lines are automatically stripped for backward compatibility

Changes

• New: UdfCompiler — compiles UDF sources and packages into JAR using javax.tools.JavaCompiler
• New: MavenDependencyResolver — parses //JDEPS and resolves artifacts via Mima embedded Maven resolver
• New: JavaUdfPreprocessor — replaces JBangPreprocessor, auto-detects .java files extending Flink UDF classes
• Deleted: JBangRunner, JBangPreprocessor and their tests
• Updated: Dockerfiles (removed JBang image stage and PATH), templates (removed shebang), Spring wiring

Test plan

• 30 new unit tests (UdfCompilerTest, JavaUdfPreprocessorTest, MavenDependencyResolverTest)
• All 94 sqrl-cli tests pass
• Full build passes (207 integration tests, 0 failures)
• Container IT (JavaUdfContainerIT) — requires Docker image rebuild

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 61.93182% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 13.27%. Comparing base (76b9af1) to head (799da83).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...i/src/main/java/com/datasqrl/util/UdfCompiler.java	67.76%	33 Missing and 6 partials ⚠️
...ava/com/datasqrl/util/MavenDependencyResolver.java	36.58%	25 Missing and 1 partial ⚠️
.../src/main/java/com/datasqrl/util/SqrlInjector.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1969      +/-   ##
============================================
+ Coverage     13.11%   13.27%   +0.16%     
  Complexity      780      780              
============================================
  Files           592      593       +1     
  Lines         16848    16908      +60     
  Branches       1971     1974       +3     
============================================
+ Hits           2210     2245      +35     
- Misses        14435    14459      +24     
- Partials        203      204       +1     

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[velo]

UDF Container Test Performance

	JBang (before)	JavaCompiler (after)	Speedup
JavaUdfContainerIT	111.5s	19.0s	5.8x faster

From CircleCI logs — same test, same Docker container setup, just the UDF compilation path changed.