Add jws-diag instances command: detect all running Tomcat instances via /proc

[onkar717]

Summary

• Adds InstanceScanner that scans all /proc/*/cmdline entries for the Bootstrap class and returns every running Tomcat process (sorted by PID ascending), unlike the existing ProcessDetector which returns only the first
• Adds TomcatInstance value object (PID, catalinaHome, catalinaBase)
• Adds instances sub-command with --format human|json output
• Human output: table of PID / CATALINA_HOME / CATALINA_BASE columns
• JSON output: array of {pid, catalinaHome, catalinaBase} objects
• Zero changes to existing config model or parser code

Design decisions

• InstanceScanner is public with a package-accessible constructor accepting a Path procRoot for deterministic unit tests (no live /proc needed)
• CATALINA_BASE defaults to CATALINA_HOME when -Dcatalina.base is absent (matches Tomcat startup behaviour)
• Directories that exist at scan time but disappear mid-read are silently skipped (TOCTOU-safe)

Test plan

• InstanceScannerTest synthetic /proc tree: zero instances, one instance, multiple instances, unreadable entries, missing flags
• InstancesHumanFormatterTest golden snapshot for 0 / 1 / N instances
• InstancesJsonFormatterTest golden snapshot for 0 / 1 / N instances
• mvn verify passes (394 tests, 0 failures)

[onkar717]

@dsoumis

[dsoumis]

Test plan claims "unreadable entries" tested but no such test exists