docs: add Java support to setup skill, optimize skill, and stop hook

[mashraf-222]

Summary

• skills/setup/SKILL.md: Filled in the empty Java config section (Check 1c) with full configuration discovery instructions — detecting source/test roots, writing codeflash.* properties to pom.xml (Maven) or gradle.properties (Gradle)
• skills/optimize/SKILL.md: Added Java build files (pom.xml, build.gradle) to the "Correct cwd" section so the optimizer finds the right project root for Java projects
• scripts/suggest-optimize.sh: Added HAS_JAVA_CHANGES detection and a Java message block. Previously .java files were detected in git log but silently ignored — now they properly trigger the optimization suggestion

Test plan

• Verified no test regressions — all pre-existing failures are identical on unmodified main (8 tests fail due to script simplification, not this change)
• bats tests/test_suggest_optimize.bats passes same 19/27 tests as main

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