<!-- Node: follows H4 (#718) --> ## Description Remove the `@vue/compat` package and migrate any remaining Vue 2-era APIs to native Vue 3. This unblocks running on a clean Vue 3 build without the compatibility layer. ## Background `@vue/compat` has been carrying Vue 2 API support since the initial Vue 3 migration. Issue #718 (Vue 2 API cleanup pass) is now closed. The shim can be removed once all remaining compat warnings are resolved. ## Approach 1. Enable `compatConfig: { MODE: 3 }` globally to surface all remaining compat warnings at runtime 2. Work through each warning category (lifecycle renames, `$set`/`$delete`, filters, etc.) until clean 3. Remove `@vue/compat` from `package.json`; let `vue: ^3` run natively 4. Run full test suite and verify no regressions ## Acceptance Criteria - `@vue/compat` removed from `package.json` - No Vue compat warnings at runtime - 75 test suites still passing - No functional regressions in UI