feat: library_import_local, library_update_metadata, library_remove_tag Rust commands for local file import and metadata editing

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fix: library.rs - remove unused warnings (dead code, unused variables)

fix: add real library palette extraction and remove stale color path

fix: add library_add_web_reference function and fix board_add_image internal call

feat: library.rs - add library_remove_item and library_add_tag commands

fix: make hover overlay, shield popup, and settings actually work

feat: library.rs - add library_remove_item and library_add_tag commands

Add persistence session download stubs for Phase 3 alpha

Fix library lifetime and unused import

Fix Shield popover airspace and add Phase 3 library board core