test: remove low-value coverage

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Summary

• remove tests that only prove static existence, typed structure, visual implementation, or mock behavior
• consolidate broad registry, keybinding, component, and command tests around observable runtime contracts
• replace the Sheets migration golden harness with focused resolver, selection, and cell-transformation tests
• document every changed test file and the remaining gaps in TEST_SUITE_AUDIT.md

Result

• normal suite: 185 → 157 test files and 1,491 → 1,157 cases
• deleted 31 test files, added 3 focused contract files, and rewrote or consolidated 27 files
• removed 334 Vitest/Node cases plus 6 Playwright cases
• removed 9 obsolete snapshot, golden-data, and parity-harness artifacts

Verification

• pnpm check
• pnpm build:pages
• pnpm --filter blocks test:e2e — 25 passed
• pnpm pack:local

Nx marked @constructive-io/registry:test as flaky during the full check, although all 17 registry tests passed.