Move Settings legal links to the page footer

[bradleymackey]

Summary

• replace the boxed Settings legal section with a semantic page footer
• reuse the shared bare Terms, Privacy, and Security links without adding them back to the sidebar
• add integration coverage for footer placement and the absence of card styling and explanatory copy

Testing

• go test -count=1 ./internal/server
• DATABASE_URL='postgres://track:track@localhost:5436/track?sslmode=disable' go test -count=1 -run 'TestUISettingsPageUpdatesProfileAndPassword|TestPublicLegalPagesAndLinks' ./internal/server

Closes TRACK-42.