release: FixMap v0.8.4

[aryamthecodebreaker]

Summary

• bump CLI, core, Action, web dependency, lockfile, and MCP server metadata to 0.8.4
• document the Doctor/ancestor-shadow fix and verified isolated-prefix installation flow
• pin README Action and installation examples to v0.8.4

Release evidence

• 417 workspace tests pass
• typecheck, lint, production builds, and zero-vulnerability production audit pass
• Action metadata/bundle parity, server manifest, smoke tests, and scanner benchmark pass
• held-out: 7/12 Top-1, 8/12 Top-3, 9/12 Top-5
• external: 11/16 Top-1, 16/16 Top-3 and Top-5
• adversarial: 8/8, false-confidence rate 0
• CLI and core npm tarball dry-runs report 0.8.4