feat: custom process type overrides

[productdevbook]

Summary

• Adds processTypeOverrides Defaults key to persist user-defined process type mappings
• PortInfo.active() now checks for overrides before auto-detecting process type
• Context menu on every port row includes a "Set Process Type" submenu with all types
• "Reset to Auto" option clears the override and restores automatic detection
• Overrides are per process name, so all ports from the same process share the type

Fixes #68

Test plan

• Right-click a port → "Set Process Type" → select a different type
• Verify the type badge and sidebar category update after next scan refresh
• Verify "Reset to Auto" restores the original detected type
• Verify override persists across app restarts
• Verify Docker subprocesses can be recategorized as requested in the issue

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