Remove all alternate update paths — fleet redeploy is release + upgrade all

Killed:
- rebuild_and_restart (in-container cargo self-compile): the MCP tool,
  the `rebuild` chat command in all four transports, the web-ui bot
  command, and the underlying function. This was the path that caused
  the exec() deadlocks.
- upgrade_sled gateway MCP tool: second entry point to sled upgrades,
  defaulted to serving the gateway's own macOS binary to Linux sleds.
- GET /api/huskies-binary (both sled and gateway route trees): served
  current_exe(), wrong platform when the gateway is macOS. Superseded
  by /api/artifacts/ which now also serves on the gateway route tree.
- `huskies upgrade` CLI subcommand and --source flag: third way of
  doing the same download-and-replace. Escape hatch for a bricked sled
  is `docker cp` + restart.

Kept, distinct jobs: `project-rebuild` (container/image updates),
`rebuild gateway` + script/local-release (gateway self-update).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019fHdm92yjvguPi2LiXfLB9

server/src/http/mcp/tools_list/mod.rs

@@ -78,7 +78,6 @@ mod tests {
         assert!(names.contains(&"get_server_logs"));
         assert!(names.contains(&"prompt_permission"));
         assert!(names.contains(&"get_pipeline_status"));
-        assert!(names.contains(&"rebuild_and_restart"));
         assert!(names.contains(&"get_token_usage"));
         assert!(names.contains(&"move_story"));
         assert!(names.contains(&"unblock_story"));
@@ -117,7 +116,7 @@ mod tests {
         assert!(names.contains(&"convert_item_type"));
         assert!(names.contains(&"edit"));
         assert!(names.contains(&"write"));
-        assert_eq!(tools.len(), 85);
+        assert_eq!(tools.len(), 84);
     }
 
     #[test]

server/src/http/mcp/tools_list/system_tools.rs

@@ -42,14 +42,6 @@ pub(super) fn system_tools() -> Vec<Value> {
                 "properties": {}
             }
         }),
-        json!({
-            "name": "rebuild_and_restart",
-            "description": "Rebuild the server binary from source and re-exec with the new binary. Gracefully stops all running agents before restart. If the build fails, the server stays up and returns the build error.",
-            "inputSchema": {
-                "type": "object",
-                "properties": {}
-            }
-        }),
         json!({
             "name": "prompt_permission",
             "description": "Present a permission request to the user via the web UI. Used by Claude Code's --permission-prompt-tool to delegate permission decisions to the frontend dialog. Returns on approval; returns an error on denial.",