dashboard: surface a distinct 'lemond missing / inference unavailable' degraded state

[thinmintdev]

What to build

When Lemonade is absent (placeholder-SHA skip, or a non-fatal tarball download failure), nothing tells the user inference is unavailable — chat just 502s / times out. SlotManager + dashboard should report a distinct "inference unavailable — lemond missing" degraded state.

Pointers: installer/install.sh:1117. Audit 0.4 / Q4.4.

Acceptance criteria

• SlotManager detects lemond-absent and exposes a distinct degraded status (API)
• Dashboard renders an explicit "inference unavailable (lemond missing)" state instead of opaque chat timeouts
• Verified by simulating an install with Lemonade absent

Blocked by

None - can start immediately