refactor: retire legacy dashboard workbenches

[douglasmonsky]

Summary

• convert Investigator, Compression Lab, Cache and Context, Diagnostics, and Reports to one notice-only compatibility route
• preserve 0.24.x CLI, HTTP, export, and full-profile MCP compatibility without loading retired UI jobs or page chunks
• localize compatibility copy across all 12 supported dashboard locales
• enforce compatibility-only route inventory and bundle-removal contracts

Verification

• frontend: 609 tests passed
• dashboard release candidate: 14 Chromium tests passed
• i18n: 148 tests passed
• compatibility notice: 11 tests passed
• dashboard verify and release readiness passed
• final read-only review: 1 finding, 1 accepted and fixed