Enable DOGFOOD_FLAGS for OSS and add fix-it suggestion for failed commands

Two changes addressing agent context visibility and error recovery:

1. Enable DOGFOOD_FLAGS in oss.rs — this activates AgentViewBlockContext,
   which auto-attaches user-executed command output (stdout/stderr/exit code)
   to the AI conversation context. Previously the LLM was blind to any
   commands the user ran via `!` prefix in agent view.

2. Add instant "Fix this error" prompt suggestion when a user-run command
   fails (non-zero exit) in agent view. This lets users hand off errors to
   the agent with one click instead of manually copy-pasting output.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/bin/oss.rs

@@ -24,6 +24,7 @@ fn main() -> Result<()> {
             mcp_static_config: None,
         },
     );
+    state = state.with_additional_features(galaxy_core::features::DOGFOOD_FLAGS);
     if cfg!(debug_assertions) {
         state = state.with_additional_features(galaxy_core::features::DEBUG_FLAGS);
     }